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NCER Solutions For Class 10 Science 2020 Chapter Wise

NCERT Class 10 model questions and solutions for the same are provided in this page for science. Practise of these questions will help the students to understand the concepts even better and score well in the exams. The chapters in science are divided into Part A, B and C. Part A consists of Multiple Choice Questions, Part B consists of Short Answer type questions and Part C consists of Long Answer type questions. The chapters with questions of different types are given below.

Chapter 1 : Chemical Reactions and Equations

Part A : Multiple Choice Questions

1. Which of the following is not a physical change?

1. Boiling point of water to give water vapour
2. Melting point of ice to give water
3. Dissolution of salt in water
4. Combustion of Liquified Petroleum Gas(LPG)

Answer : d

2. The following reaction is an example of a 4NH₃ (g) + 50₂ (g) à 4NO (g) + 6 H₂ O (g)

1. 1. Displacement Reaction
   2. Combination Reaction
   3. Redox Reaction
   4. Neutralisation Reaction
      1. 1. 1 and 4
         2. 2 and 3
         3. 1 and 3
         4. 3 and 4

Answer : c

Explanation :

A redox reaction is combination of oxidation (removal of hydrogen) and reduction (addition of hydrogen). Displacement reaction involves displacement of some part of a compound with other atom like H atoms of NH₃ are displaced by oxygen.

3. Which of the following statements about the given reaction are correct?

3 Fe(s) + 4 H₂O (g) à Fe₃O (s) + 4 H₂ (g)

1. 1. 1. Iron metal is getting oxidised.
      2. Water is getting reduced.
      3. Water is acting as reducing agent.
      4. Water is acting as oxidizing agent.
         1. 1. 1, 2 and 3
            2. 3 and 4
            3. 1, 2 and 4
            4. 2 and 4

Answer : c

Explanation: Addition of oxygen to Fe is an oxidation process whereas lose of oxygen from H₂O to H₂ is a reduction step. Since water is source of oxygen therefore it acts as oxidizing agent.

4. Which of the following are exothermic processes?

1. 1. Reaction of water with quick lime
   2. Dilution of an acid
   3. Evaporation of water
   4. Sublimation of camphor (crystals)
      1. 1. 1 and 2
         2. 2 and 3
         3. 1 and 4
         4. 3 and 4

Answer : a

Explanation : Energy is released in exothermic reactions in the form of heat.

5. Three beakers labelled as A, B and C each containing 25ml of water were taken. A small amount of NaOH, anhydrous CuSO₄ and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is (are) correct?

1. 1. In beakers A and B, exothermic process has occurred.
   2. In beakers A and B, endothermic process has occurred.
   3. In beaker C, exothermic process has occurred.
   4. In beaker C, endothermic process has occurred.
      1. 1. Only 1
         2. Only 2
         3. 1 and 4
         4. 2 and 3

Answer : c

Explanation: For an exothermic reaction, heat releases during reaction so temperature increases whereas endothermc reactions proceed with absorption of heat which decrease the temperature of reaction.

6. A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?

1. KmnO₄ is an oxidizing agent, it oxidizes FeSO₄
2. FeSO₄ acts as an oxidizing agent and oxidizes KmnO₄
3. The colour disappears due to dilution, no reaction is involved.
4. KmnO₄ is an unstable compound and decomposes in the presence of FeSO₄ to a colourless compound.

Answer : a

Explanation : Potassium permanganate (KmnO₄) acts as good oxidizing agent in acidic medium and reduces itself to manganese (II) cations, Mn²⁺. It oxidizes FeSO₄ to Fe₂(SO₄)_3.

7. Which among the following is (are) double displacement reaction(s) ?

1. 1. 1. 1. 1. Pb + CuCl₂ à PbCl₂ + Cu
            2. Na₂SO₄ + BaCl₂ à BaSO₄ + 2NaCl
            3. C + O₂ à CO₂
            4. CH₄ + 2O₂ à CO₂ + 2H₂O
               1. 1. (i) and (iv)
                  2. Only (ii)
                  3. (i) and (ii)
                  4. (iii) and (iv)

Answer : b

Explanation :

A double displacement reaction involves displacement of two ions of two different compounds that results the formation of new compounds.

8. Which among the following statement (s) is or are true? Exposure of silver chloride to sunlight for a long duration turns grey due to –

1. 1. 1. 1. 1. The formation of silver by decomposition of silver chloride.
            2. Sublimation of silver chloride
            3. Decomposition of chlorine gas from silver chloride
            4. Oxidation of silver chloride.
               1. 1. (i) only
                  2. (i) and (iii)
                  3. (ii) and (iii)
                  4. Only (iv)

Answer : a

Explanation :

In the presence of sunlight, AgCl decompose to form grayish white silver metal and releases chlorine gas.

9. Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is are true about asking slaking of lime and the solution formed?

1. It is an endothermic reaction
2. It is exothermic reaction
3. The pH of the resulting solution will be more than seven.
4. The pH of the resulting solution will be less than seven.
   1. (i) and (ii)
   2. (ii) and (iii)
   3. (i) and (iv)
   4. (iii) and (iv)

Answer : b

Explanation :

The formation of calcium hydroxide from calcium oxide and water with heat so it is an exothermic reaction. Calcium hydroxide is a basic compound so pH will be more than 7.

10. Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

1. Displacement reaction
2. Precipitation reaction
3. Combination reaction
4. Double displacement reaction
   1. Only (i)
   2. Only (ii)
   3. Only (iv)
   4. (ii) and (iv)

Answer : d

Explanation :

Double displacement reaction involves displacement of cation and anions of two different compounds. In given reaction, precipitate of barium sulphate is formed.

11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is

1. 1:1
2. 2:1
3. 4:1
4. 1:2

Answer : b

Explanation :

The balance chemical equation for electrolysis of water is;

Electric current

2H₂O(1) --------------------à 2H₂(g) + O₂(g)

12. Which of the following is (are) an endothermic process(es) ?

1. Dilution of sulphuric acid
2. Sublimation of dry ice
3. Condensation of water vapours
4. Evaporation of water
   1. Both (i) and (iii)
   2. Only (ii)
   3. Only (iii)
   4. Both (ii) and (iv)

Answer : d

Explanation :

An endothermic process involves absorption of heat such as sublimation and evaporation needs heat energy.

13. In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?

1. Lead sulphate (insoluble)
2. Lead acetate
3. Ammonium nitrate
4. Potassium sulphate

Answer : b

Explanation :

For the formation of lead iodide some soluble salt of lead is required like lead acetate which will form lead iodide with potassium acetate.

14. Which of the following gases can be used for storage of fresh sample of an oil for a long time?

1. Carbon dioxide or oxygen
2. Nitrogen or oxygen
3. Carbon dioxide or helium
4. Helium or nitrogen

Answer : d

Explanation :

Inert gases like Helium and Nitrogen can be used for storage of food items as they prevent the oxidation of food items.

15. The following reaction is used for the preparation of oxygen gas in the laboratory

Heat

2KC1O₃(s)----------------à 2KC1 (s) + 3O₂(g)

Catalyst

Which of the following statement(s) is/are correct about the reaction?

1. 1. It is a decomposition reaction and endothermic in nature
   2. It is a combination reaction
   3. It is a decomposition reaction and accompanied by release of heat
   4. It is a photochemical decomposition reaction and exothermic in nature

Answer : a

Explanation : Decomposition reaction can be defined as the reaction which involves decomposition of one compound to more than one substance. Endothermic reactions require heat energy to form products.

12. Which one of the following processes involve chemical reactions?

1. Storing of oxygen gas under pressure in a gas cylinder
2. Liquefaction of air
3. Keeping petrol in a China dish in the open
4. Heating copper wire in the presence of air at high temperature

Answer : d

Explanation : Chemical changes involve formation of new compounds from one or more substances. Reaction of copper wire with oxygen forms copper (ii) oxide.

17. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?

1. 2H₂(I) + O₂(I) à 2H₂O (g)
2. 2H₂(g) + O₂(I) à 2H₂O (g)
3. 2H₂(g) + O₂(g) à 2H₂O (I)
4. 2H₂(g) + O₂(g) à 2H₂O (g)

Answer : c

Explanation :

At standard conditions, hydrogen and oxygen exist in gaseous state whereas water in liquid state.

18. Which of the following are combination reactions?

Heat

1. 2 KC1O₃--------------à 2 KC1 + 3 O₂
2. MgO + H₂O à Mg (OH)₂
3. 4Al + 3O₂ à 2Al₂O₃
4. Zn + FeSO₄ à ZnSO₄ + Fe
   1. Both (i) and (iii)
   2. Both (iii) and (iv)
   3. Both (ii) and (iv)
   4. Both (ii) and (iii)

Answer : d

Explanation :

Combination reactions form a new product with the combination of more than one reactant molecules.

Part B : Short Answer Type

19. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

1. Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
2. Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
3. Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂SO₄.
4. Ethane is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

Answer :

Catalyst

1. 1. 1. 1. 1. N₂(g) + 3H₂(g) ----------à 2 NH₃ (g)

773K

This is an example of combination reaction.

1. 1. 1. 1. 2. NaOH (aq) + CH₃COOH (I) --à CH₃COONa (aq) + H₂O(l)

This is an example of neutralization reaction as well as double displacement reaction.

Conc. H₂SO₄

3. C₂H₅OH (1) + CH₃COOH (I) -----------------à CH₃COOC₂H₅(1) + H₂O (I)

This is an example of double displacement reaction and also called as esterification.

4. 2C₂H₆ (g) + 7O₂ (g) -à 4 CO₂(g) + 6 H₂O (g)

This is an example of combustion reaction.

20. Write the balanced chemical equation for the following reactions and identify the type of reaction in each case.

1. In thermite reaction, iron (iii) oxide reacts with aluminium and gives molten iron and aluminium oxide.
2. Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
3. Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
4. Ethanol is burnt in air to form carbon dioxide, water and releases heat.

Answer : ∆

1. 1. 1. 1. 1. Fe₂ O₃(s) + 2 Al(S) ----------à 2Fe (I) + Al₂ O₃

This is an example of displacement and redo

∆

1. 1. 1. 1. 2. 3Mg (s) + N₂(g) -----à Mg₃N₂(s)

This is an example of combination reaction.

1. 1. 1. 1. 3. 2KI(aq) + Cl₂ (g) ----à 2 KCl(aq) + I₂ (s)

This is an example of redox and displacement reaction.

d. C₂H₅OH(I) + 3O₂(g) -----à 2CO₂ (g) + 3 H₂O + Heat

This is an example of combustion reaction.

21. Complete the missing components given as X and Y in the following.

1. Pb(NO₃)₂ (aq) + 2 Kl (aq) à PbI₂ (X) + 2KNO₃ + (Y)
2. Cu (s) + 2AgNO₃ (aq) à Cu (NO₃)₂ (aq) + X(s)
3. Zn(s) + H₂SO₄(aq) à ZnSO₄(X) +H₂(Y)

x

1. 4. CaCO₃(s)------à CaO(s) + CO₂(g)

Answer:

1. 1. Pb(NO₃)₂ (aq) + 2 Kl (aq) à PbI₂ (s) + 2KNO₃ + (aq)
   2. Cu (s) + 2AgNO₃ (aq) à Cu (NO₃)₂ (aq) + 2Ag(s)
   3. Zn(s) + H₂SO₄(aq) à ZnSO₄(aq) +H₂(g)

Heat

1. 4. CaCO₃(s)----------à CaO(s) + CO₂(g)

22. Which among the following changes are exothermic or endothermic in nature?

1. Decomposition of ferrous sulphate
2. Dilution of sulphuric acid
3. Dissolution of sodium hydroxide in water
4. Dissolution of ammonium chloride in water

Answer :

1. 1. 1. 1. 1. Decomposition of ferrous sulphate absorbs heat during reaction therefore it is an example of endothermic reaction.
            2. When we dissolve sulphuric acid in water, large amount of heat is liberated so it is an exothermic reaction.
            3. When we dissolve sodium hydroxide in water, large amount of heat is liberated so it is an exothermic reaction.
            4. Mixing of ammonium chloride in water absorbs heat from reaction mixture therefore it is an example of endothermic reaction.

23. Identify the reducing agent in the following reactions.

1. 4NH₃ + 5O₂ à 4NO + 6H₂O
2. 2H₂O + 2F₂ à 4HF + O₂
3. Fe₂O₃ + 3CO à 2Fe + 3CO₂
4. 2H₂ + O₂à 2H₂O

Answer:

a. NH₃ is the reducing agent as it gives hydrogen to O_2.

b. H₂O is the reducing agent.

c. CO is a reducing agent.

d. H₂ is the reducing agent.

24. Identify the oxidant in the following reactions.

1. 2Mg + O₂ à 2MgO
2. CuO + H₂ à Cu + H₂O

Answer:

a. Since O₂ provides oxygen, it is the oxidant.

b. CuO is the oxidant as it is reduced to Cu.

25. Write the balanced chemical equations for the following.

a. Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.

b. Sodium hydrogen carbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.

c. Copper sulphate on treatment with potassium iodide precipitates cuprous iodide, liberates iodide gas and also forms potassium sulphate.

Answer:

a. Na₂CO₃(s) + HCl (aq) à NaCl (aq) + NaHCO₃ (aq)

b. NaHCO₃ (s) + HCl (aq) à NaCl (aq) + H₂O(l) + CO₂(g)

c. 2CuSO₄(s) + 4Kl(aq)à Cu₂l₂ + I₂ (g) + 2K₂SO₄(aq)

26. A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction.

Answer :

The solution of KCl with AgNO₃ form white precipitate of AgCl. This is a double displacement reaction.

KCl (aq) + AgNO₃ (aq) à AgCl (s) + KNO₃ (aq)

27. Ferrous sulphate decomposes with the evolution of a gas having a characteristics odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer:

2FeSO₄(s) à Fe₂O₃(s) + SO₂(g) + SO₃(g)

The heating of ferrous sulphate gives ferric oxide and mixture of sulphur dioxide and sulphur trioxide gas. This is an example of thermal decomposition reaction and the odour of burning sulphur is due to SO₂ gas.

28. Why do fire flies glow at night?

Answer:

Fire flies have a luminous bag which contains a protein; luciferin. The oxidation of luciferin occurs in the presence of luciferare enzyme with emission of light which occurs due to oxidation of magnesium. Hence they glow at night.

29. grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or physical change?

Answer :

After plucking grapes from plants, fermentation of sugar is carried out in the presence of yeast which changes sugar to ethanol and carbon dioxide. This process occurs in the absence of oxygen means in anaerobic conditions.

Whereas grapes attach to plant involve in aerobic respiration and no fermentation can be possible under aerobic conditions.

Here fermentation is a chemical change as it results the formation of new substances; alcohol and carbon dioxide.

30. Which among the following are physical or chemical changes?

1. 1. Evaporation of petrol
   2. Burning of LPG
   3. Heating of an iron rod to red hot
   4. Curdling of milk
   5. Sublimation of solid ammonium chloride

Answer :

1. Physical change
2. Chemical change
3. Physical change
4. Chemical change
5. Physical change

31. During the reaction of some metals with dilute hydrochloric acid, following observations were made.

1. Silver metal does not show any change.
2. The temperature of the reaction mixture rises when aluminium (Al) is added.
3. The reaction of sodium metal is found to be highly explosive.
4. Some bubbles of a gas are seen when lead is reacted with the acid.

Explain these observations giving suitable reasons.

Answer :

1. The reactivity of silver is very low as it is placed below hydrogen in reactivity series so it does not react with dilute hydrochloric acid.
2. Aluminium reacts with dilute HCl to form Aluminium chloride with hydrogen gas. It is an exothermic reaction so temperature of reaction mixture rises.
3. Sodium is an alkali metal which is one of the most reactive metals and readily reacts with dilute HCl to form NaCl and hydrogen gas. The evolution of hydrogen gas cause explosion.
4. Reaction of lead metal with dilute HCl forms lead (II) chloride and releases hydrogen gas in the form of bubbles. Since reaction is quite slow due to less reactivity of lead, only bubbles of H₂ are seen to evolve.

32. A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer :

The substance X is calcium oxide (CaO) which is also known as quick lime. Reaction of quick lime with water forms calcium hydroxide. It is an alkaline solution and easily turns red litmus to blue.

CaO(s) + H₂O -> Ca(OH)₂

33. Write a balanced chemical equation for each of the following reactions and also classify them.

a. Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

b. A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

c. Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.

d. Hydrogen sulphate gas reacts with oxygen gas to form solid sulphur and liquid water.

Answer:

a. Pb (CH3COO)₂ (aq) + 2HCl (dil) --> PbCl₂(s) + 2CH₃COOH(aq)

This is a double displacement and a precipitation reaction.

b. 2C₂H₅OH(I) + 2Na(s) --> 2C₂H₅O^-Na⁺ + H₂

This is a displacement reaction.

c. Fe₂O₃(s) + 3CO(g) --> 2Fe(s) + 3CO₂ (g)

This is an example of redox reaction.

d. 2H₂S(g) + O₂ (g) --> 2S (s) + 2 H₂O(I)

This is an example of redox reaction.

34. Why do we store silver chloride in dark coloured bottles?

Answer:

Silver chloride can decompose in the presence of light to form silver metal therefore it must store in dark coloured bottles which can interrupt the path of light and prevent the decomposition of silver chloride.

The photochemical decomposition of silver chloride is shown below;

2AgCl(s)---------> 2Ag(s) + Cl₂(g)

35. Balance the following chemical equation and identify chemical reaction the type of chemical reaction.

a. Mg(s) + Cl(g) --> MgCl₂(s)

b. H₂O₂ (I) --------> H₂O + O2(g)

Answer:

a. Mg(s) + Cl₂(g) --> MgCl₂(s) (Combination reaction)

b. 2H₂O₂ (I) -----> 2H₂O (l) + O₂(g) (Photochemical reaction)

36. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.

a. Write the chemical formulae of X and Y.

b. Write a balanced chemical equation, when X is dissolved in water.

Answer:

a. The chemical formulae of X=MgO; Y=Mg₃N₂

b. MgO + H₂O --> Mg (OH)₂

37. Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain, why?

Answer:

Zinc is placed above hydrogen in reactivity series therefore it can replace hydrogen from HCl and form hydrogen gas.

Zn + 2HCl --> ZnCl₂ + H₂

Whereas copper is placed below hydrogen in reactivity series therefore it cannot replace hydrogen from dilute acid and does not release hydrogen gas from dilute hydrochloric acid.

Cu + HCl --> No reaction

38. A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.

a. Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.

b. Name the black substance formed and gives its chemical formula.

Answer:

a. The metal surface of silver article reacts with atmosphere sulphur compounds like hydrogen sulphide and form black layer of sulphides. This phenomenon is called as corrosion or tarnishing of silver.

b. The black substance that is formed by the reaction of hydrogen sulphide and atmospheric oxygen is silver sulphide (Ag₂S).

Part C : Long Answer Type

39. On heating blue coloured podwer of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed.

a. Write a balanced chemical equation of the reaction.

b. Identify the brown gas X evolved.

c. Identify the type of reaction.

d. What could be the pH range of aqueous solution of the gas X.

Answer:

1. 1. 1. 1. 1. 2Cu (NO₃)₂ --à 2CuO + O₂ + 4NO₂
            2. X is nitrogen dioxide gas that is evolved as brown, choking fumes.
            3. A thermal decomposition reaction.
            4. The aqueous solution of the NO₂ forms nitrous acid and nitric acid so pH of solution would be less than 7 as medium will be acidic.

40. Give the characteristic tests for the following gases.

a. CO₂

b. SO₂

c. O₂

Answer:

a.CO₂ gas : When gas is passed through lime water; it forms insoluble calcium carbonate which turns the solution milky. This is called as lime water test.

CO₂ + H₂O + CaCO₃ à Ca (HCO₃)₂

b.SO₂ gas: Due to acidic nature, sulphur dioxide gas turn moist litmus paper from blue to red. It also changes the orange colour of acidified potassium dichromate solution to green.

K₂Cr_2­O₇ + 3SO₂ + H₂SO₄ à Cr₂ (SO₄)₃ + K₂SO₄ + H₂O

c. O2 gas: Oxygen gas burns brightly with wooden splinter that proves the combustible nature of oxygen gas.

C +O₂ à CO₂ + Heat + Light

41. What happens when a piece of

a. Zinc metal is added to copper sulphate solution?

b. Aluminium metal is added to dilute hydrochloric acid?

c. silver metal is added to copper sulphate solution?

Answer :

a.When zinc metal is added to copper sulphate solution, the colour of copper sulphate solution disappears and coloursless zinc sulphate solution is formed. Solid brown copper is deposited as it displaces by Zn.

b. Aluminium displaces hydrogen from HCl and hydrogen gas is evolved with soluble aluminium chloride.

c. Silver is a Nobel metal and does not exhibit any reaction with copper sulphate.

42. What happens when zinc granules are treated with dilute solution of NaCl and NaOH, also write chemical equation.

NaCl solution :

No reaction will take place as sodium is more reactive than Zn and cannot replace by it.

Zn(s) + NaCl (aq) à No reaction

NaOH solution :

Zinc reacts with NaOH solution and form sodium tetrahydroxidozincate and hydrogen gas.

Zn + 2NaOH + 2H­_2­O à Na₂ [Zn(OH₄)] + H₂

43. On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.

a. Write a balanced chemical equation of the reaction involved.

b. What other name can be given to this precipitation reaction?

c. On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?

Answer:

a.Na₂SO₃(aq) + BaCl₂(aq) àBaSO₃(s) + 2NaCl (aq)

b.Double displacement reaction

c.Addition of HCl dissolves the white precipitate of BaSO₃ and form soluble BaCl₂.

44. You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃ and H₂O. In which of the containers these solutions can be kept?

Answer :

1. Reations of copper with
   1. Dilute HCl

Copper exhibits no reaction with HCl so it can be stored in copper container.

1. 2. Dilute HNO₃

With dilute nitric acid, copper metal forms copper nitrate with nitric oxide and water so dilute nitric acid cannot be stored in copper container.

1. 3. H₂O

There is no reaction between water and copper metal at room temperature so water can be stored in copper container.

2. Reactions of aluminium with
   1. Dilute HCl

Aluminium reacts with Al reacts with dilute HCl and form aluminium chloride with hydrogen gas so it cannot be stored in aluminium container.

1. 2. Dilute HNO₃

Nitric acid is an oxidizing agent and in the presence of it, aluminium metal forms a protective layer of oxide so it will not react further. Hence dilute nitric acid can be stored in aluminium container.

1. 3. H₂O

At room temperature, there will be no reaction between aluminium metal and water so it can be stored in aluminium container.

Chapter 2 : Acid, Base and Salt

Part A : Multiple Choice Questions

1.What happens when a solution of an acid is mixed with a solution of a base in a test tube?

(i)The temperature of the solution increases.

(ii) The temperature of the solution decreases.

(iii)The temperature of the solution remains the same.

(iv)Salt formation takes place.

1. 1. 1. 1. 1. 1. 1. 1. Only (i)
                     2. (i) and (iii)
                     3. (ii) and (iii)
                     4. (i) and (iv)

Answer : d

Explanation:

The reaction of acid and base is an exothermic reaction and results the formation of salt and water.

2. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?

a. Baking powder

b. Lime

c. Ammonium hydroxide solution

d. Hydrochloric acid

Answer : d

Explanation:

Alkaline solutions turn red litmus paper to blue. Excess of acid will reverse the changes so we have to add excess of hydrochloric acid which turns the solution acidic.

3. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to

a. Absorb the evolved gas

b. Moisten the gas

c. Absorb moisture from the gas

d. Absorb CI^- ions from the evolved gas.

Answer : c

Explanation:

Calcium chloride is a good dehydrating agent so it is used to absorb moisture from the hydrogen chloride gas.

4. Which of the following salts does not contain water of crystallisation?

a. Blue vitriol

b. Baking soda

c. Washing soda

d. Gypsum

Answer : b

Explanation:

1. • Blue vitriol = CuSO4 . 5H2O
   • Baking soda = NaHCO3
   • Washing soda = Na2CO3. 10H2O
   • Gypsum= CaSO4 . 2H2O

5. Sodium carbonate is a basic salt because it is a salt of

a. Strong acid and strong base

b.weak acid and weak base

c. strong acid and weak base

d.weak acid and strong base

Answer : d

Explanation:

Sodium carbonate is the salt of carbonic acid and sodium hydroxide. Here NaOH is a strong base and carbonic acid is a weak acid.

6. Calcium phosphate is present in tooth enamel. Its nature is

a. basic

b.acidic

c. neutral

d.amphoteric

Answer :a

Explanation:

Calcium phosphate is salt of weak acid and strong base so it is a basic salt.

7. A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish blue?

a. lemon juice

b.vinegar

c. common salt

d. an antacid

Answer : d

Explanation:

pH paper gives greenish blue colour in weak alkaline medium so antacid which is an alkaline compound will show greenish blue color on pH paper.

8. Which of the following gives the correct increasing order of acid strength?

a. water < acetic acid < hydrochloric acid

b. water < hydrochloric acid >acetic acid

c. acetic acid < water < hydrochloric acid

d. hydrochloric acid < water < acetic acid

Answer : a

Explanation:

Water is a natural substance, hydrochloric acid is a strong acid as it ionizes completely in water, whereas acetic acid ionizes only partially in water, hence, it is a weak acid.

9. If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done?

a. Wash the hand with saline solution.

b. Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.

c. After washing with plenty of water applies solution of sodium hydroxide on the hand.

d. Neutralise the acid with a strong alkali.

Answer : b

Explanation:

Use of sodium hydrogen carbonate neutralizes the effect of acid completely.

10. Sodium hydrogen carbonate when added to acetic acid evolve a gas. Which of the following statements are true about the gas evolved?

(i) It turns lime water milky.

(ii)It extinguishes a burning splinter.

(iii)It dissolves in a solution of sodium hydroxide.

(iv)It has a pungent odour.

(i) and (ii)

(i), (ii) and (iii)

(ii), (iii) and (iv)

(i) and (iv)

Answer : b

Explanation:

Reaction of sodium hydrogen carbonate with acetic acid forms sodium acetate and water with carbon dioxide (CO2) gas

11. Common salt besides being used in kitchen can also be used as the raw material for making

(i) washing soda

(ii) bleaching powder

3. baking soda
4. slaked lime

a. (i) and (ii)

b. (i), (ii) and (iv)

c. (i), (ii) and (iii)

d. (i), (iii) and (iv)

Answer : c

Explanation:

Common salt is used as a raw material for manufacturing of sodium hydroxide, washing soda, bleaching powder, baking soda, hydrochloric acid, chlorine, etc.

12. One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is

a. Hydrochloric acid

b. Tartaric acid

c. Acetic acid

d. Sulphuric acid

Answer : b

Explanation:

Baking powder is a mixture of sodium hydrogen carbonate and a weak edible acid named as tartaric acid.

13. To protect tooth decay we are advised to brush our teeth regularly. The nature of the tooth paste commonly used is

a. acidic

b. neutral

c. basic

d. corrosive

Answer : c

Explanation:

The tooth paste commonly used is alkaline or basic in nature. So they can neutralize the effect of extra acids present in mouth cavity which are mainly responsible for tooth decay.

14. Which of the following statements is correct about an aqueous solution of an acid and a base?

(i) Higher the pH, stronger the acid

(ii) Higher the pH, weaker the acid

(iii) Lower the pH, stronger the base

(iv) Lower the pH, weaker the base

1. 1. 1. 1. 1. (i) and (iii)
            2. (ii) and (iii)
            3. (i) and (iv)
            4. (ii) and (iv)

Answer : d

Explanation:

The pH value lie between 0 to 14 in which 0 to 7 is acidic medium and 7 to 14 is alkaline or basic medium.

15. The pH of the gastric juices released during digestion is

a. less than 7

b. more than 7

c. equal to 7

d. equal to 0

Answer : a

Explanation:

Hydrochloric acid is produced by our stomach during digestion.

16. Which of the following phenomena occur, when a small amount of acid is added to water?

(i) Ionisation

(ii) Neutralisation

(iii) Dilution

(iv) Formation

a. (i) and (ii)

b.(i) and (iii)

c. (ii) and (iii)

d. (ii) and (iv)

Answer : b

Explanation:

Ionization can be defined as the dissociation of molecule into its respective ions. Mixing of an acid with water decreases the concentration of acid and is called as dilution.

17. Which one of the following can be used as an acid-base indicator by a visually impaired student?

a. Litmus

b. Turmeric

c. Vanilla essence

d. petunia leaves

Answer : c

Explanation:

An olfactory indicator is required for visually impaired student. Vanilla essence imparts different smell in different medium so can be used for such students.

18. Which of the following substances will not give carbon dioxide on treatment with dilute acid?

a. Marble

b. Limestone

c. Baking soda

d. Lime

Answer : d

Explanation:

Marble or lime stone and baking soda release CO2 with HCl but lime with HCl form CaCl2 and water.

19. Which of the following is acidic in nature?

a.lime juice

b. human blood

c. lime water

d. antacid

Answer : a

Explanation:

Lime juice contains citric acid and so acidic in nature.

20. In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus (figure) was set up.

Which among the following statement is correct?

1. Bulb will not glow because electrolyte is not acidic.
2. Bulb will glow because NaOH is a strong base and furnishes ions for conduction.
3. Bulb will not glow because circuit is incomplete.
4. Bulb will not glow because it depends upon the type of electrolytic solution.
   1. 1. 1. 1. 1. 1. 1. (i) and (iii)
                     2. (ii) and (iv)
                     3. Only (ii)
                     4. Only (iv)

Answer : c

Explanation:

Strong acids or bases are good conductors of electricity because they ionize completely in aqueous solution to give ions.

21. Which of the following is used for dissolution of gold?

a. Hydrochloric acid

b. Sulphuric acid

c. Nitric acid

d. Aqua-regia

Answer : d

Explanation:

Aqua-regia is a very strong acid and can be used to dissolve gold. It is a 1:3 mixture of concentrated HNO3 and concentrated HCl.

22. Which of the following is not a mineral acid?

a. Hydrochloric acid

b. Citric acid

c. Sulphuric acid

d. Nitric acid

Answer : b

Explanation:

Mineral acids are mainly prepared from the minerals present in the earth’s crust so they are also called as inorganic acids like HCl, H2SO4 and HNO3. Organic acids are produced from plants or animals and contain carbon atoms like acetic acid and citric acid.

23. Which among the following is not a base?

a. NaOH

b.KOH

c. NH4OH

d. C2H5OH

Answer : d

Explanation:

C2H5OH is an organic compound with -OH functional group that is known as alcohol. It cannot give OH- ions in its solution.

24. Which of the following statements is not correct?

a. All metal carbonates react with acid to give a salt, water and carbon dioxide.

b. All metal oxides react with water to give salt and acid.

c. Some metals react with acids to give salt and hydrogen.

d. Some non-metal oxides react with water to form an acid.

Answer : b

Explanation:

Some of the metal oxides react with water to form alkali like sodium oxide reacts with water to form sodium hydroxide.

25.Match the chemical substances given in Column I with their appropriate application given in Column II.

Answer : c

Explanation:

• Bleaching powder (CaOCl2) – used for bleaching or decolorisation of clothes.
• Baking soda (NaHCO3) – used as an antacid for relieving stomach acidity.
• Washing soda (Na2 CO3) – used in preparation of glass.
• Sodium chloride (NaCl) – Used for production of H2 and Cl2 gases.

26.Equal volumes of hydrochloric acid and sodium hrdroxide solutions of same concentration are mixed and the pH of the resulting solution is checked with a pH paper. What would be the colour obtained?

a. Red

b. Yellow

c. Yellowish green

d. Blue

Answer : c

Explanation :

Hydrochloric acid and sodium hrdroxide are strong acid and base respectively. So mixing of strong acid and strong base will form neutral salt and water giving the pH value as 7.

27. Which of the following is /are true when HCl(g) is passed through water?

(i) it does not ionise in the solution as it is a covalent compound

(ii) it ionises in the solution

(iii) it gives both hydrogen and hydroxyl ion in the solution.

(iv)it forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule.

1. 1. 1. 1. 1. Only (i)
            2. Only (iii)
            3. (ii) and (iv)
            4. (iii) and (iv)

Answer : c

Explanation:

HCl being a polar covalent compound which can easily ionize in water to form hydronium ions (H3O+) and chloride ions (Cl-).

28. Which of the following statement is true for acids?

a. bitter and change red litmus to blue

b. sour and change red litmus to blue

c. sour and change blue litmus to red

d. bitter and change blue litmus to red

Answer : c

Explanation :

Acids have sour taste and can turn blue litmus solution to red.

29. Which of the following are present in a dilute aqueous solution of hydrochloric acid?

a. H3O⁺ + Cl^-

b. H3O⁺ + OH –

c. Cl- + OH-

Answer : a

Explanation :

A strong acid like HCl dissociates completely in its aqueous solution and form hydronium ions with its respective anion.

30. Identify the correct representation of reaction occurring during chloralkali process.

Answer : d

Explanation :

Chlor-alkali process is an industrial process that is used to form sodium hydroxide by electrolysis of aqueous solution of sodium chloride. It forms sodium hydroxide with hydrogen and chlorine gas as by-products.

Part B : Short Answer Type

31. Match the acids given in Column I with their correct source given in Column II.

Answer :

32. Match the important chemicals given in Column I with the chemical formulae given in Column II.

Answer :

33. What will be the action of the following substances on litmus paper?

Dry HCl gas, moistened NH3 gas, lemon juice, carbonated soft drink, curd, soap solution.

Answer :

• Dry HCl gas : It will show no effect on litmus paper as no ionization will occur in gaseous state.
• Moistened NH3 gas : It is alkaline in nature so red litmus will turn blue.
• Lemon juice : It contains citric acid therefore it turns blue litmus to red.
• Carbonated soft drinks : They have carbonic acid which is a weak acid and can turns blue litmus to red.
• Curd : It contains lactic acid so blue litmus will turn red.
• Soap solution: They are alkaline in nature and can turn red litmus to blue.

34. Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

Answer :

Acid present in ant sting is formic acid which is also named as Methanoic acid. Chemical formula for formic acid is HCOOH. It is acidic in nature, so an alkaline compound like wet baking soda can be used to neutralize its effect to get relief from discomfort.

35. What happens when nitric acid is added to egg shell?

Answer :

Calcium carbonate is main component of egg shell so when we add nitric acid to egg shell, it reacts with calcium carbonate to form soluble calcium nitrate and water with brisk effervescence of carbon dioxide gas.

36. A student prepared solutions of (i) an acid and (ii) a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?

Answer :

Other than litmus paper, pH indicators can also be used to distinguish between an acidic and an alkaline solution. Some common pH indicators are methyl orange, phenolphthalein. They show characteristic colour change in acidic and alkaline medium. Some natural indicators such as turmeric, red cabbage juice can also used to identify acidic and alkaline behavior of solutions.

37. How would you distinguish between baking powder and washing soda by heating?

Answer :

Baking soda is sodium hydrogen carbonate (NaHCO3) which forms sodium carbonate (Na2CO3), water and carbon dioxide gas while heating.

Presence of CO2 can be detected with the help of lime water which turns milky after reacting with carbon dioxide gas.

Washing soda is sodium carbonate deca-hydrate which means there are 10 water molecules present with crystal hence named as water of crystallization.

On heating washing soda, it becomes anhydrous and presence of water of crystallization can be detected with the help of anhydrous CuSO4 which shows colour change from white to blue with moisture.

38. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water turns it milky. Identify A, B and C.

Answer :

Salt which is used in bakery product is baking soda or sodium hydrogen carbonate. On heating of baking soda, sodium carbonate is formed with evolution of carbon dioxide gas.

Sodium carbonate is used to remove hardness of water. Another product is carbon dioxide gas that gives lime test in which it turns lime water milky.

Thus, A = NaHCO3 ; B= Na2CO3 and C=CO2.

39. In one of the industrial processes for manufacture of sodium hydroxide, a gas X is formed as by-product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved.

Answer :

Sodium hydroxide is manufactured by electrolysis of aqueous solution of sodium chloride which forms hydrogen and chlorine gas as byproducts. Reaction of chlorine gas with lime water forms bleaching powder. Thus, X=Cl2 gas and Y=Calcium oxychloride.

The equation for the preparation of sodium hydroxide (NaOH) and bleaching powder is given below:

1. 2NaCl(aq) + 2H2O(I) à 2NaOH(aq) + Cl2 (g) + H2 (g)
2. Cl2 (g) + Ca(OH)2 à CaOCl2 + H2O

40. Fill in the missing data in the given table.

Answer :

41. What are strong and weak acids? In the following list of acids, separate strong acids from weak acids.

• Hydrochloric acid
• Citric acid
• Acetic acid
• Nitric acid
• Formic acid
• Sulphuric acid

Answer :

Strong acids ionize completely in its aqueous solution therefore such acids contains high concentration of hydronium ions in their solutions. Nitric acid, sulphuric acid are good examples of strong acids.

Unlike strong acids, weak acids cannot ionize completely therefore solution of a weak acid contains some un-ionized molecules with its ions. Organic acids like citric acid, acetic acid are weak acids.

In the given acids;

• Hydrochloric acid – strong acid
• Citric acid – weak acid
• Acetic acid – weak acid
• Nitric acid – strong acid
• Formic acid – weak acid
• Sulphuric acid – strong acid

42. When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.

Answer :

Zinc is a metallic element. Metals react with dilute solutions of strong acids to form respective salts and hydrogen gas.

The reaction of zinc with dilute solution of strong acid like HCl forms zinc chloride (ZnCl2) and hydrogen gas is evolved.

Zn + 2HCl à ZnCl2 + H2

Hydrogen gas is used in hydrogenation of vegetable oil. It can be tested with the help of burning splinter as it burns with a pop sound.

Part C : Long Answer Type

43. In the following schematic diagram for the preparation of hydrogen gas as shown in the figure, what would happen if the following changes are made?

a.In place of zinc granules, same amount of zinc dust is taken in the test tube.

b.Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.

c.In place of zinc, copper turnings are taken.

d. Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.

Answer :

a.Since zinc dust has larger surface area than zinc granules, so reaction will be faster and hydrogen gas will evolve with greater speed.

b.Both hydrochloric acid and sulphuric acid are strong acids so almost same amount of gas is evolved.

c.Copper is a less reactive metal and does not react with dilute acids so there will be no reaction between copper turnings and dilute HCl.

d.Reaction of zinc with sodium hydroxide forms sodium zincate (Na2Zn02) with evolution of hydrogen gas.

44. For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake.

a. How will it affect the taste of the cake and why?

b. How can baking soda be converted into baking powder?

c. What is the role of tartaric acid added to baking soda?

Answer :

a.Baking soda is sodium hydrogen carbonate which decomposes to sodium carbonate, water and carbondioxide on heating. Baking powder is a mixture of sodium hydrogen carbonate with tartaric acid which readily reacts with sodium carbonate and neutralizes it. Therefore use of baking soda will give a bitter taste to cake due to presence of sodium carbonate.

b.Baking powder is formed by addition of tartaric acid to baking soda.

c.Presence of tartaric acid in baking powder neutralizes the effect of sodium carbonate formed during decomposition of baking soda.

45. A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y; it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G and Z.

Answer :

Here X is calcium carbonate which is a metal carbonate which reacts with dilute HCl to form calcium carbonate (CaCO3), water and carbon dioxide gas.

When carbon dioxide gas is passed through lime water or calcium hydroxide it gives the calcium carbonate back. So Y is calcium hydroxide.

Brine is saturated solution of sodium chloride (NaCl). Electrolysis of brine forms hydrogen gas at cathode and chlorine gas at anode.

So G is chlorine gas which is passed through dry calcium hydroxide, produces bleaching powder, CaOCl2 (Z).

Hence X=Calcium carbonate, Y=Lime water, G= Chlorine gas and Z=Calcium oxychloride or bleaching powder.

46. A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a product of chlor-alkali process. Identify B, what type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

Answer :

Here common base B is sodium hydroxide which is hygroscopic and absorbs moisture from the atmosphere. It is also formed as a product of chlor-alkali process. Chlor-alkali process is electrolysis of brine (saturated solution of sodium hydroxide) that forms aqueous sodium hydroxide with hydrogen gas and chlorine gas.

Reaction of sodium hydroxide with acidic oxide like carbon dioxide forms salt (sodium carbonate) and water.

47. A sulphate salt of group 2 element of the periodic table is a white, soft substance, which can be molded into different shapes by making its dough. When this compound is left in open for sometime, it becomes a solid mass and cannot be used for molding purposes. Identify the sulphate salt and why does it show such a behaviour? Give the reaction involved.

Answer :

The sulphate salt which can be molded into different shapes by making its dough is calcium sulphate hemi-hydrate. It is commonly known as plaster of Paris. Here, two molecules of calcium sulphate share one molecule of water.

Because of presence of water crystallization, it is soft.

It readily reacts with atmospheric moisture and forms hard solid mass. This solid mass is known as gypsum. Conversion of plaster of Paris to gypsum can be represented as given below:

48. Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.

Answer :

X must be a compound which forms water with acids. It means it must be a base which reacts with acids to form salt and water. This base also reacts with zinc metal and releases hydrogen gas. So it must be NaOH.

Chapter 3 : Metals and Non-Metals

Part A : Multiple Choice Questions

1. Which of the following property is generally not shown by metals?

a. electrical conduction

b. sonorous in nature

c. dullness

d. ductility

Answer : c

Explanation :

Metallic luster is the characteristic feature of metals that is due to presence of free electrons.

2. The ability of metals to be drawn into thin wire is known as :

a. ductility

b. malleability

c. sonorousity

d. conductivity

Answer : a

Explanation :

Ductility can be defined as the property of metals to drawn in thin wires by application of force on them.

3. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?

(i) good thermal conductivity

(ii) good electrical conductivity

(iii)ductility

(iv)high melting point

a. (i) and (ii)

b. (i) and (iii)

c. (ii) and (iii)

d. (i) and (iv)

Answer : d

Explanation :

Some of the most common properties of Aluminium are good thermal conductivity, malleability, light weight and high melting point which make it useful for making cooking utensils.

4. Which one of the following metals do not react with cold as well as hot water?

a. Na

b. Ca

c. Mg

d. Fe

Answer : d

Explanation :

Na, Ca and Mg are reactive metals and quickly react with water. At room temperature, the reaction of Fe is very slow but red hot iron reacts with steam to form Fe3O4 with hydrogen gas.

3Fe + 4H2O à Fe3O4 + 4H2

5. Which of the following oxide of iron would be obtained on prolonged reaction of iron with steam?

a. FeO

b. Fe2O3

c. Fe3O4

d. Fe2O3 and Fe3O4

Answer : c

Explanation :

Prolong heating of red hot iron with steam form Fe3O4 with hydrogen gas.

3Fe + 4H2O à Fe3O4 + 4H2

6. What happens when calcium is treated with water?

1. it does not react with water.
2. it reacts violently with water.
3. it reacts less violently with water.
4. Bubbles of hydrogen gas formed stick to the surface of calcium.

a. (i) and (iv)

b. (ii) and (iii)

c. (i) and (ii)

d. (iii) and (iv)

Answer : d

Explanation :

Calcium reacts less violently with water producing the bubbles of hydrogen gas along with calcium hydroxide (Ca(OH)2).

7. Generally metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?

a. H2SO4

b. HCl

c. HNO3

d. All of these

Answer : c

Explanation :

Nitric acid is a strong oxidizing agent so it does not give hydrogen gas with metals (except Mn and Mg). As hydrogen gas is formed in the reaction HNO3 oxidizes this hydrogen to water.

8. The composition of aqua regia is

a. Dil.HCl : Conc.HNO3 <-> 3:1

b. Conc.HCl : Dil.HNO3 <-> 3:1

c. Conc.HCl : Conc.HNO3 <-> 3:1

d. Dil.HCl : Dil.HNO3 <-> 3:1

Answer : c

Explanation :

Aqua-regia is a mixture of concentrated HCl and concentrated HNO3 in 3:1 ratio.

9. Which of the following are not ionic compounds?

(i) KCl

(ii) HCl

(iii) CCl4

(iv) NaCl

a. (i) and (ii)

b. (ii) and (iii)

c. (iii) and (iv)

d. (i) and (iii)

Answer : b

Explanation :

Ionic compounds are formed by combination of cation and anions. HCl and CCl4 are formed by equal sharing of electrons between atoms in the molecule. Here HCl is a polar covalent compound and CCl4 is a non-polar covalent compound.

10. Which one of the following properties is not generally exhibited by ionic compounds?

a. solubility in water

b. electrical conductivity in solid state

c. high melting and boiling points

d. electrical conductivity in molten state

Answer : b

Explanation :

Ionic compounds can conduct electricity in molten or aqueous state due to presence of free ions. In solid state, no free or mobile ions are available for conducting electricity.

11. Which of the following metals exist in their native state in nature?

(i) Cu

(ii) Au

(iii) Zn

(iv) Ag

a. (i) and (ii)

b. (ii) and (iii)

c. (ii) and (iv)

d. (iii) and (iv)

Answer : c

Explanation :

Gold and silver (Au and Ag) are also known as Noble metals as they are less reactive and exist in their native state in nature.

12. Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?

(i) Au

(ii) Cu

(iii) Na

(iv)K

a. (i) and (ii)

b. (i) and (iii)

c. (ii) and (iii)

d. (ii) and (iv)

Answer : a

Explanation :

Alkali metals are very reactive so cannot refine with the help of electrolytic refining process.

13. Silver articles become black on prolonged exposure to air. This is due to the formation of

a.Ag3N

b.Ag3O

c.Ag2S

d.Ag2S and Ag3N

Answer : c

Explanation :

Silver metals reacts with atmospheric sulphur compounds like H2S gas and form black coating of Ag2S over surface.

14. Galvanisation is a method of protecting iron from rusting by coating it with a thin layer of

a. Gallium

b. Aluminium

c. Zinc

d. Silver

Answer : c

Explanation :

Zinc metal is used to protect iron surface from rusting.

15. Stainless steel is very useful material, for our life. In stainless steel, iron is mixed with

a. Ni and Cr

b. Cu and Cr

c. Ni and Cu

d. Cu and Au

Answer : a

Explanation :

Stainless steels are formed with the addition of high proportion of chromium and nickel to iron.

16. If copper is kept open in air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of

a. CuSO4

b.CuCO3

c.Cu(NO3)2

d. CuO

Answer : b

Explanation :

Copper reacts with moist carbon dioxide in the air and form green colour basic copper carbonate.

17. Generally metals are solid in nature. Which one of the following metals is found in liquid state at room temperature?

a. Na

b. Fe

c. Cr

d. Hg

Answer : d

Explanation :

At room temperature, mercury is found in liquid state.

18. Which of the following metals are obtained by electrolysis of their chlorides in molten state?

(i) Na

(ii) Ca

(iii) Fe

(iv) Cu

1. 1. 1. 1. 1. 1. 1. 1. (i) and (iv)
                     2. (iii) and (iv)
                     3. (i) and (iii)
                     4. (i) and (ii)

Answer : d

Explanation :

Usually alkali and alkaline earth metals can be extracted by electrolysis of their salts in molten state.

19. Generally non-metals are not lustrous. Which of the following non-metals is lustrous?

a. Sulphur

b. Oxygen

c. Nitrogen

d. Iodine

Answer : d

Explanation :

Iodine is a non-metal with lustrous appearance and exists in solid state.

20. Which one of the following four metals would be displaced from the solution of its salts by other three metals?

a. Mg

b. Ag

c. Zn

d. Cu

Answer : b

Explanation :

Least reactive metal can be displaced from its solution by other three metals. Silver is least reactive out of given four metals.

21. 2ml each of conc. HCl, HNO3 and a mixture of conc.HCl and conc.HNO3 in the ratio of 3:1 were taken in test tubes labeled as A,B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C. The metal could be

a. Al

b. Au

c. Cu

d. Pt

Answer : b, d

Explanation :

A mixture if conc. HCl and conc. HNO3 in the ratio of 3:1 forms aqua-regia which can dissolve gold and platinum.

22. An alloy is

a. an element

b. a compound

c. a homogeneous mixture

d. a heterogenous mixture

Answer : c

Explanation :

A homogeneous mixture of different metals or a non-metals is called as alloy.

23. An electrolytic cell consists of

(i) positively charged cathode

(ii) negatively charged anode

(iii) positively charged anode

(iv) negatively charged cathode

a. (i) and (ii)

b. (iii) and (iv)

c. (i) and (iii)

d. (ii) and (iv)

Answer : b

Explanation :

There is a positivity charged anode and negatively charged cathode in an electrolytic cell.

24. During electrolytic refining of zinc, it gets

a. deposited on cathode

b. deposited on anode

c. deposited on cathode as well as anode

d. remains in the solution

Answer : a

Explanation :

During electrolytic refining the pure zinc metal is deposited on cathode.

25. An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following.

a. Mg

b. Na

c. P

d. Ca

Answer : b

Explanation :

Sodium is a soft, reactive alkali metal.

26.Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metals as one of its constituents?

a. Brass

b. Bronze

c. Amalgam

d. Steel

Answer : d

Explanation :

1. 1. 1. 1. 1. Brass – copper and zinc
            2. Bronze – copper and tin
            3. Amalgam – mercury with other metals
            4. Steel – iron with carbon

27. Which among the following statements is incorrect for magnesium metal?

a. It burns in oxygen with a dazzling white flame.

b. It reacts with cold water to form magnesium oxide and evolves hydrogen gas.

c. It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas.

d. It reacts with steam to form magnesium hydroxide and evolves hydrogen gas.

Answer : b

Explanation :

Magnesium metal does not react with cold water but reacts with both hot water and steam to form magnesium hydroxide and hydrogen gas.

28. Which among the following alloys contain mercury as one of its constituents?

a. Stainless steel

b. Alnico

c. Solder

d. Zinc amalgam

Answer : d

Explanation :

1. 1. 1. 1. 1. 1. 1. 1. Stainless steel – Fe with C
                     2. Alnico – Al, Ni and Co
                     3. Solder – Pb and Sn
                     4. Zinc amalgam – Zn with Hg

29. Reaction between X and Y forms compound Z. X loses electron and Y gains electron. Which of the following properties is not shown by Z?

a. Has high melting point

b. Has low melting point

c. Conducts electricity in molten state

d. Occurs as solid

Answer : b

Explanation :

Since Z is formed from X and Y by complete transfer of electrons therefore Z should be ionic compound which must have high melting point and conductivity in molten state and usually occur as solids.

30. The electronic configurations of three elements X, Y and Z are X-2, 8 : Y-2,8,7 and Z-2,8,2. Which of the following is correct?

a. X is a metal

b. Y is a metal

c. Z is a non-metal

d. Y is a non-metal and Z is a metal

Answer : d

Explanation :

Metals have 1 or 2 electrons in their valence shell whereas non-metals have 5-7 valence electrons. Here X has octet configuration so it should be a noble gas.

31. Although metals form basic oxides, which of the following metals form an amphoteric oxide?

a. Na

b.Ca

c.Al

d.Cu

Answer : c

Explanation :

Some of the metals like Aluminium metal forms amphoteric oxide (Al2O3) which can behave like acid as well as base.

32. Generally non-metals are non-conductors of electricity. Which of the following is a good conductor of electricity?

a. diamond

b. graphite

c. sulphur

d. fullerene

Answer : b

Explanation :

Graphite is one of the allotropes of carbon which shows layers arrangement of carbon atoms. The fourth valence electron of each carbon is free to move that makes it good conductor of electricity.

33. Electrical wires have a coating of an insulating material. The material, generally used is

a. sulphur

b.graphite

c.PVC

d. all can be used

Answer : c

Explanation :

An insulating substance is required to coat the electrical wire such as PVC.

34. Which of the following non-metals is a liquid?

a. carbon

b. bromine

c. phosphorus

d. sulphur

Answer : b

Explanation :

Bromine is a non-metal which exists in liquid state.

35. Which of the following can undergo a chemical reaction?

a. MgSO4 + Fe

b. ZnSO4 + Fe

c. MgSO4 + Pb

d. CuSO4 + Fe

Answer : d

Explanation :

According to reactivity series, more reactive metal can displace less reactive metal from its compound. Fe is more reactive compare to copper so it can displace copper from its compound, copper sulphate. The reactivity order for given metals are;

Mg < Zn < Fe < Pb < Cu

36. Which one of the following figures correctly describes the process of electrolytic refining?

Answer : c

Explanation :

In electrolytic refining process, impure metal forms the anode which is positive electrode whereas pure metal forms the cathode which is negative electrode. In the given image, apparatus for electrolytic refining of copper metal is being shown in which copper from impure anode dissolves into the solution and Cu²⁺ ions from the solution are deposited on the cathode.

Part B : Short Answer Type

37. Iqbal treated a lustrous, divalent element M with sodium hydroxide. He observed the formation of bubbles in reaction mixture. He made the same observations when this element was treated with hydrochloric acid. Suggest how can be identify the produced gas. Write chemical equations for both the reactions.

Answer :

The divalent element must be some metal which releases hydrogen gas with both acid and bases. Bring a burning splinter near the gas, it will burn with a pop sound, hence it must be hydrogen gas. The divalent element could be zinc. Chemical equations for both the reactions are;

38. During extraction of metals, electrolytic refining is used to obtain pure metals.

a. Which material will be used as anode and cathode for refining of silver metal by this process?

b. Suggest a suitable electrolyte also.

c. In this electrolytic cell, where do we get pure silver after passing electric current?

Answer :

1. Thin strip of pure silver is made the cathode and impure silver block is made the anode.
2. Any salt solution of silver like AgNO3 can be used as electrolyte.
3. On passing electric current, from the electrolyte metal ions discharge on the cathode whereas metal ions from impure metal dissolves and goes into the electrolyte solution.

39. Why should the metals sulphides and carbonated be converted to metal oxides in the process of extraction of metal from them?

Answer :

Usually metal sulphides and carbonates are converted to metal oxides in the process of extraction of metal. This is because metal oxides can easily reduce to metal with the help of some common reducing agent like coke.

Ores of metal can be converted to metal oxides with the help of calcination or roasting which depends on the nature of ore. For example, metal carbonate can convert to metal oxide by calcinations whereas roasting is used for metal sulphide.

40. Generally when metals are treated with mineral, acids. Hydrogen gas is liberated but when metals (except Mn and Mg) are treated with HNO3, hydrogen is not liberated, why?

Answer :

Unlike other acids, reaction of nitric acid is little different because it is a good oxidizing agent. As hydrogen gas is formed during the reaction of nitric acid with metals, acid reacts with hydrogen gas and converts it to water. And nitric acid gets reduced to NO2 or NO or N2O.

41. Compound X and aluminium are used to join railway tracks.

a. Identify the compound X

b. Name the reaction

c. Write down its reaction

Answer:

1. Iron(III) oxide (Fe2O3) is used with aluminium (Al) to join railway tracks.
2. The reaction is known as thermite reaction or alumino thermy process.
3. Fe2O3(s) + 2Al(s) à 2Fe(I) + Al2O3(s) + Heat

42. When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (molecular mass = 40) and liberates a gas Z which easily catches fire. Identify X, Y and Z and also write the reaction involved.

Answer :

Given molecular formula of Y = XOH

And molecular mass of Y = 40

So atomic mass of metal X would be:

M+16+1 =40

M=40-17

M= 23

Metal with atomic mass 23 is sodium and reaction of it with cold water will form sodium hydroxide (NaOH).

2Na + 2H2O (cold) à 2NaOH +H2

Hence; X = Sodium (Na), Y= Sodium hydroxide (NaOH), Z=Hydrogen gas (H2)

43. A non-metal X exists in two different forms Y and Z. Y is hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y and Z.

Answer:

Different forms of any element are called as allotropes. Since Y is the hardest substances so it must be diamond which is an allotrope of carbon. Hence non-metal X is carbon. Another allotrope of carbon is graphite which is very good conductor of electricity due to presence of free mobile electrons.

Hence X=Carbon, Y= Diamond and Z=Graphite

44. The following reaction takes place when aluminium powder is heated with MnO2.

3MnO2(s) + 4Al(s) 3Mn(I) + 2Al2O3(I) +Heat

1. Is aluminium getting reduced?
2. Is MnO2 getting oxidized?

Answer :

1. As Al converts to Al2O3 i.e oxygen is added to Al so it is getting oxidized.
2. Now MnO2 gets converted to Mn, i.e. oxygen is being removed from MnO2, so it is getting reduced.

45. What are the constituents of soldier alloy? Which property of solder makes it suitable for wedding electrical wires?

Answer:

Solder is a fusible metal alloy of lead (Pb) and tin(Sn). It contains 40% lead and 60% of Sn metal.

Solder has a low melting point around 90^o C to 450^oC as compared to the metals used in forming electrical wires. So, it acts as bridge between two metal pieces, hence used for welding electrical wires.

46. Metal A which is used in thermite process, when heated with oxygen gives an oxide B, which is amphoteric in nature. Identify A and B. Write down the reactions of oxide B with HCl and NaOH.

Answer :

Aluminium (Al) is used in thermite process so metal A is Aluminium. The reaction of Al with oxygen forms aluminium oxide Al2O3 which is amphoteric in nature as it can exhibit acidic as well as basic nature.

4Al(s) + 3O2 (g) à 2Al2O3(s)

Hence, A = aluminium and B=Aluminium oxide

Reactions of aluminium oxide with HCl and NaOH are as given below;

Al2O3(s) + 6HCl (a) à 2AlCl3(aq) + 3H2O(I)

Al2O3(s) + 2NaOH(aq) à 2NaAlO2(aq) + H2O(I)

47. A metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore. Give the reactions involved.

Answer :

Mercury is the only metal which exists in liquid state at room temperature. It is usually extracted from its sulphide ore, mercury II sulphide or cinnabar (HgS) by the process of roasting. Hence;

Metal = Mercury and Ore =Cinnabar

Roasting of ore occurs in the presence of air and form metal oxide which further reduce to metal.

48. Give the formulae of the stable binary compounds that would be formed by the combination of following pairs of elements.

a. Mg and N2

b. Li and O2

c. Al and Cl2

d. K and O2

Answer :

1. Mg and N2 – Mg3N3 (Magnesium nitride)
2. Li and O2 – Li2O (Lithium oxide)
3. Al and Cl2 – AlCl3 (Aluminium chloride)
4. K and O2 – K2O (Potassium oxide)

49. What happens when

a. ZnCO3 is heated in the absence of oxygen?

b. A mixture of Cu2O and Cu2S is heated?

Answer :

1. Heating of carbonate ores in the absence of oxygen is called as calcinations. Zinc carbonate also forms zinc oxide and carbon dioxide when it is heated in the absence of oxygen. This process is used to convert carbonate ores to metal oxides and also helps to remove moisture and volatile impurities.
2. Reaction of copper sulphide and copper oxide at high temperature forms copper metal and sulphur dioxide gas is expelled out.

50. A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming.

a. Identify A, B and C.

b. To which group of periodic table does A belong?

Answer :

1. Non-metal A must be carbon as it forms two oxides; carbon monoxide and carbon dioxide. Out of these two oxides; one is toxic that is CO and another is responsible for global warming so it must be CO2.

Hence ; A= carbon, B= carbon monoxide and C=carbon dioxide

2. The electronic configuration of carbon is 2, 4. So there are 4 valence electrons and group number should be 10+ number of valence electrons. So carbon belongs to 14^th group of the periodic table.

51. Give two examples each of the metals that are good conductors and comparatively poor conductors of heat respectively.

Answer :

1. Good conductors: Aluminium and copper are good conductors of heat.
2. Poor conductors: Titanium and mercury are poor thermal conductors.

52. Name one metal and one non-metal that exists in liquid state at room temperature. Also name two metals having melting point less than 310 K.

a. Metal that exists in liquid state at room temperature = Mercury.

b. Non-metal that exists in liquid state at room temperature = Bromine.

c. Metals having melting point less than 310K = Caesium (28.5^o) and Gallium (29.76^o C)

53. An element A reacts with water to form a compound B which is used in white washing. The compound B on heating forms an oxide C which on treatment with water gives back B. Identify A, B and C and give the reactions involved.

Answer :

The compound that is used in white wash is calcium hydroxide. So the element must be calcium that reacts with water to form calcium hydroxide. Heating of calcium hydroxide forms calcium oxide which again converts to hydroxide with the reaction of water.

Hence A = Ca, B =Ca(OH)2, C=CaO

Reactions involved are:

54. A metal M does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify M and black coloured product and also explain the reaction of M with oxygen.

Answer :

Because of less reactivity, copper metal does not release hydrogen gas with acid.

Cu(s) + HCl à No reaction

Hence metal M is copper.

Reaction of copper with oxygen on prolonged heating to form a black substance copper II oxide.

2Cu(s) + O2(g) à 2CuO(s)

55. An element forms an oxide A2O3 which is acidic in nature. Identify A as a metal or non-metal.

Answer :

Metals usually form basic oxides like BaO, MgO, Na2O etc. Unlike metals, non-metals tend to form acidic oxides.

As we move from left to right in the periodic table, the acidity of oxides increases. So the element which forms acidic oxide must be non-metallic element.

The formula for oxide is A2O3 means the charge on element must be +3 or element should have 3 valence electrons that is boron and formula for oxide would be B2O3.

56. A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in term of reactivity. Write the equation of the reaction involved.

Answer :

In reactivity series, iron is placed above copper. So we can say that iron is more reactive compare to copper and it can displace copper from its compounds. When copper sulphate solution is placed in an iron pot, iron reacts with copper sulphate and form iron sulphate with copper.

So the blue colour of copper sulphate solution fade of light green due to formation of iron sulphate and holes are produced at places where iron metals has reacted.

Fe(s) + CuSO4(aq) à FeSO4(aq) + Cu(s)

Part C : Long Answer Type

57. A non metal A which is the largest constituent of air, when heated with H2 in 1:3 ratio in the presence of catalyst (Fe) gives a gas B. On heating with O2 it gives an oxide C. If this oxide is passed into water in the presence of air, it gives an acid D which acts as a strong oxidising agent.

a. identify A, B , C and D

b. To which group of the periodic table does this non-metal belongs?

Answer :

1. The largest cosntituent of air is nitrogen gas so the A must be nitrogen gas. Reaction of nitrogen with hydrogen in the presence of Fe catalyst forms ammonia gas. It is known as Haber process.

Ammonia reacts with water to give nitric oxide which further oxidized to form NO2.

Reaction of oxides with water in the presence of air results nitric acid.

4NO2 + H2O +O2 à 4HNO3

Hence A=nitrogen, B=ammonia, C=nitrogen dioxide and D=nitric acid.

2. Nitrogen has electronic configuration 2,5. Thus with having 5 valence electrons, nitrogen belongs to group 15 of periodic table.

58. Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores.

Answer :

1. Extraction of less reactive metals like mercury:

1. Roasting – Heating of metal sulphide in the presence of excess of air to form metal oxide.
2. Reduction – Metal oxide can be reduced to metal in the presence of reducing agent at high temperature.
3. Extraction of metals with medium reactivity like zinc:

(i)Roasting- Heating of metal sulphide in the presence of excess of air to form metal oxide.

(ii)Reduction- Metal oxide can be reduced to metal in the presence of reducing agent like coke or aluminium at high temperature.

59. Of the three metals X, Y and Z, X reacts with cold water, Y with hot water and Z with steam only. Identify X, Y and Z and also arrange them in order of increasing reactivity.

Answer :

X reacts with cold water so it must be very reactive like alkali metals, sodium. Sodium reacts with water to form sodium hydroxide and hydrogen gas.

2Na + 2H2O à 2NaOH + H2

Y metal can react with hot water so it must be little less reactive than X. So Y can be magnesium (Mg) which reacts with hot water to form magnesium hydroxide.

Mg + 2H2O à Mg(OH)2 + H2

Metal which reacts with steam must be iron that forms iron III oxide with steam.

3Fe + 4H2O à Fe3O4 + 4H2

Hence the increasing order of reactivity of given metals is;

Z (Fe) < Y(Mg) < X(Na)

Chapter 4 : Carbon and its Compounds

Part A : Multiple Choice Questions

1. Carbon exists in the atmosphere in the form of

a. only carbon monoxide

b. carbon monoxide in traces and carbon dioxide

c. only carbon dioxide

d. coal

Answer : c

Explanation :

Carbon exists only in the form of carbon dioxide gas (CO2) in air.

2. Which of the following statements are usually correct for carbon compounds? These

(i) Are good conductors of electricity.

(ii) Are poor conductor of electricity.

3. Have strong forces of attraction between their molecules.
4. Do not have strong forces of attraction between their molecules.

1. (i) and (iii)
2. (ii) and (iii)
3. (i) and (iv)
4. (ii) and (iv)

Answer :d

Explanation :

Carbon having four valence electrons forms only covalent compounds which exhibit less intermolecular attractions and do not have any free electrons to carry electric current. Therefore, these are poor conductors of electricity.

3. A molecule of ammonia (NH3) has

a. only single bonds

b. only double bonds

c. only triple bonds

d. two double bonds and one single bond

Answer : a

Explanation :

Ammonia is a covalent molecule in which center nitrogen atom is bonded with three hydrogen atoms through single covalent bond.

4. Buckminsterfullerene is an allotropic form of

a. phosphorus

b. sulphur

c. carbon

d.tin

Answer : c

Explanation :

Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms which are joined together in a spherical shape.

5.Which of the following are correct structural isomers of C4H10?

a. (i) and (iii)

b. (ii) and (iv)

c. (i) and (ii)

d. (iii) and (iv)

Answer : a

Explanation :

Structural isomers have same molecular formula but different parent chain of carbon atoms in the molecule.

6. In the following reaction, alkaline KmnO4 acts as:

a. reducing agent

b.oxidising agent

c. catalyst

d. dehydrating agent

Answer : b

Explanation :

KmnO4 acts as oxidising agent as it oxidized CH3CH2OH to CH3COOH by addition of oxygen atom.

7. Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

a. addition reaction

b. substitution reaction

c. displacement reaction

d. oxidation reaction

Answer : a

Explanation :

It is hydrogenation reaction means addition of hydrogen to double bonds of unsaturated compounds found in oil.

8. In which of the following compounds -OH is the functional group ?

a. butanone

b. butanol

c. butanoic

d. butanal

Answer : b

Explanation :

Compounds with -OH functional group are ended with suffix -ol.

C4H9 – OH or CH3 – CH2 – CH2 -CH2 -OH

9. The soap molecule has a

a. hydrophilic head and a hydrophobic tail

b. hydrophobic head and a hydrophilic tail

c. hydrophobic head and a hydrophobic tail

d. hydrophilic head and a hydrophilic tail

Answer : a

Explanation :

A soap molecule contains a long hydrocarbon part and a small ionic part of -COONa group. Hydrocarbon chain is hydrophobic or water repelling whereas ionic head is hydrophilic or water attracting group.

10. Which of the following is the correct representation of electron dot structure of nitrogen?

Answer : d

Explanation :

Nitrogen molecule is a covalent molecule in which two nitrogen atoms are bonded through triple covalent bond with one lone pair of electrons over each nitrogen atom.

11. Structural formula of ethyne is

Answer : a

Explanation :

General formula for alkyne is CnH2n-2. There must be at least one triple bond between carbon atoms. With two carbon atom, the possible structure would be H-C=C-H.

12. Identify the unsaturated compounds from the following.

(i) propane

(ii) propene

(iii)propyne

(iv)chloropropane

a. (i) and (ii)

b. (ii) and (iv)

c. (iii) and (iv)

d. (ii) and (iii)

Answer : d

Explanation :

Alkene and alkyne are unsaturated hydrocarbon as they have double and triple covalent bonds between carbon atoms.

13. Chlorine reacts with saturated hydrocarbons at room temperature in the

a. absence of sunlight

b. presence of sunlight

c. presence of water

d. presence of hydrochloric acid

Answer : b

Explanation :

Chlorine shows photochemical substitution reactions with saturated hydrocarbons that occurs in the presence of light.

14. In the soap micelles

a. the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

b. ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.

c. both ionic end and carbon chain are in the interior of the cluster.

d. both ionic end and carbon chain are on the exterior of the cluster.

Answer : a

Explanation :

A micelle is a spherical aggregation of soap molecules in water in which hydrocarbon ends are directed towards the centre and ionic ends are directed outwards.

15. Pentane has the molecular formula C5H12. It has

a. 5 covalent bonds

b. 12 covalent bonds

c. 16 covalent bonds

d. 17 covalent bonds

Answer : c

Explanation :

Pentane contains four C-C bonds and twelve C-H covalent bonds.

16. Structural formula of benzene is

Answer : c

Explanation :

Benzene is simplest aromatic compound with six carbon atoms and six H atoms. There are three alternate pi bonds in ring of carbon atoms.

17. Ethanol reacts with sodium and forms two products. There are

a. sodium ethanoate and hydrogen

b. sodium ethanoate and oxygen

c. sodium ethoxide and hydrogen

d. sodium ethoxide and oxygen

Answer : c

Explanation :

Ethanol reacts with sodium to form sodium ethoxide(C2H5ONa ) along with liberation of hydrogen gas.

18. The correct structural formula of butanoic acid is:

Answer : d

Explanation :

Butanoic acid is a carboxylic acid with four carbon atom and one -COOH group at terminal.

19. Vinegar is a solution of :

a. 50% - 60% acetic acid in alcohol

b. 5%-8% acetic acid in alcohol

c. 5% - 8% acetic acid in water

d. 50% - 60% acetic acid in water

Answer : c

Explanation :

Vinegar is a 5% - 8% aqueous solution of acetic acid.

20. Mineral acids are stronger acids than carboxylic acids because

(i) mineral acids are completely ionised.

(ii) carboxylix acids are completely ionised.

(iii)mineral acids are partially ionised

(iv) carboxylic acids are partially ionised.

a. (i) and (iv)

b. (ii) and (iii)

c. (i) and (ii)

d. (iii) and (iv)

Answer : a

Explanation :

Mineral acids like nitric acid, sulphuric acid are stronger than carboxylic acid as they can ionize 100% in their solution.

21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, eg. Hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

a. helium

b. neon

c. argon

d. krypton

Answer : b

Explanation :

Electronic configuration of carbon is 2, 4 hence it contains 4 valence electrons and after formation of 4 covalent bonds, it will get 4 more electrons through them so total would be 10 electrons that is atomic number for Neon gas.

22. The correct electron dot structure of a water molecule is

Answer : c

Explanation :

In water molecule, center oxygen atom contains two lone pairs of electrons and form two single covalent bonds with two hydrogen atoms.

23. Which of the following is not a straight chain hydrocarbon?

Answer : d

Explanation :

A branched chain hydrocarbon must contain some side chains which are bonded with parent carbon chain.

24. Which among the following are unsaturated hydrocarbons?

a. (i) and (iii)

b. (ii) and (iii)

c. (ii) and (iv)

d. (iii) and (iv)

Answer : c

Explanation :

Unsaturated hydrocarbons have multiple covalent bonds (double or triple bond) like alkene and alkyne.

25. Which of the following does not belong to the same homologous series?

a. CH4

b. C2H6

c.C3H8

d.C4H8

Answer : d

Explanation :

Successive members of same homologous series are differ by -CH2 unit. CH4, C2H6, C3H8 belong to same series that is of alkane and differ by -CH2 unit but C4H8 does not belong to this.

26. The name of the compound, CH3-CH2-CHO is :

a. propanal

b. propanone

c. ethanol

d. ethanal

Answer : a

Explanation :

Compound contains three carbon atoms so prop- would be root word and -CHO functional group so suffix will be -al. Hence name would be propane +al= propanal.

27. The heteroatoms present in CH3-CH2-O-CH2-CH2CL are:

(i) oxygen

(ii) carbon

(iii) hydrogen

(iv) chlorine

a. (i) and (ii)

b. (ii) and (iii)

c. (iii) and (iv)

d. (i) and (iv)

Answer : d

Explanation :

Atoms other than C and H in organic compound are called as heteroatoms.

28. Which of the following represents saponification reaction?

Answer : d

Explanation :

Saponification reaction is reaction of ester with base like NaOH to form the parent alcohol and sodium salt of carboxylic acid.

29. The first member of alkyne homologous series is:

a. ethyne

b. ethene

c. propyne

d. methane

Answer : a

Explanation :

Alkyne is an organic compound with triple covalent bond between two carbon atoms therefore first member of homologous series must have atleast two carbon atoms with one triple bond that is ethyne

Part B : Short Answer Type

30. Draw the electron dot structure of ethyne and also draw its structural formula.

Answer:

Ethyne is a hydrocarbon with molecular formula C2H2. Here two carbon atoms are bonded together by a triple covalent bond and one hydrogen atom is bonded with each carbon atom through a single covalent bond. Hence the electron dot structure of ethyne molecule can be represents as:

Structural formula of ethyne is:

31. Write the names of the following compounds.

Answer:

1. Pentanoic acid as it contains five carbon atoms with one -COOH group.
2. Pentyne as it contains five carbon atoms in a straight chain with one triple covalent bond at terminal.
3. Heptanal as it contains seven carbon atoms with one -CHO group(aldehyde group)
4. Pentanol because it contains 5 carbon atoms with one -OH group.

32. Identify and name the functional groups present in the following compounds.

Answer:

1. Functional group : -OH

Name of compound : Alcohol

2. Functional group : -COOH

Name of compound : Carboxylic acid

3. Functional group : >C = O

Name of compound : Ketone

4. Functional group : -C = C-

Name of compound : Alkene

33. A compound X is formed by the reaction of a carboxylic acid C2H4O2 and an alcohol in the presence of a few drops of H2SO4. The alcohol an oxidation with alkaline KmnO4 followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of

a. Carboxylic acid

b. Alcohol

c. The compound x. Also write the reaction.

Answer :

1. Carboxylic acid with molecular formula C2H4O2 is acetic acid or ethanoic acid having the structure as :
2. Given alcohol forms acetic acid on oxidation with alkaline KMnO4 followed by acidification. Therefore, it must be ethanol with structure CH3-CH2-OH.
3. Reaction of ethanoic acid with ethanol in presence of a few drops of conc. H2SO4 is an esterification reaction that forms an ester, ethyl ethanoate (CH3COOC2H5).

34. Why detergents are better cleansing agents than soaps? Explain.

Answer :

Detergents and soaps both are cleansing agents but detergents can be used even in hard water whereas soaps cannot use in hard water.

Soap forms an insoluble precipitate with calcium and magnesium ions found in hard water. This precipitate is called as scum which sticks to the cloths and makes the cleaning even more difficult.

On the contrary, detergents have charged ends and do not form insoluble precipitates with calcium and magnesium ions.

The cleansing action of detergents is stronger than soaps. They are more soluble in water therefore it is convenient to use them compare to soaps.

35. Name the functional groups present in the following compounds.

a. CH3COCH2CH2CH2CH3

b. CH3CH2CH2COOH

c. CH3CH2CH2CH2CHO

d. CH3CH2OH

Answer :

1. CH3COCH2CH2CH2CH3 – Ketone (>C=O)
2. CH3CH2CH2COOH – Carboxylic acid (-COOH)
3. CH3CH2CH2CH2CHO – Aldehyde (-CHO)
4. CH3CH2OH – Alcohol (-OH)

36. How is ethene prepared from ethanol? Give the reaction involved in it.

Answer :

This conversion is possible through dehydration reaction which occurs in the presence of concentrated sulphuric acid or concentrated phosphoric (V) acid, H3PO4 at 160^o C.

37. Intake of small quantity of methanol can be lethal. Comment.

Answer :

When methanol is entered in our body, it is metabolized in the liver and form formaldehyde which further converted to formate. Formate is essential for survival because it acts as building block for many biomolecules but high levels of it can cause toxicity.

Formaldehyde also reacts with living cells and can cause coagulation of protoplasm. Excess of methanol in our body also affects the optic nerve and can cause blindness.

38. A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer :

When ethanol reacts with sodium metal, it forms sodium ethoxide (C2H5O-Na+) and hydrogen gas is released. The reaction is as follows.

So the gas is hydrogen gas that is evolved during the reaction.

39. Ethene is formed when ethanol at 443K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.

Answer :

Conversion of ethanol to ethene is a dehydration reaction which occurs in the presence of excess of concentrated sulphuric acid. Here concentrated sulphuric acid acts as dehydrating agent and remove water molecule from ethanol to form ethene.

Hence concentrated sulphuric acid acts as a dehydrating agent as it removes water molecule.

40. Carbon, group (14) element in the periodic table, is known to form compounds with many elements. Write an example of a compound formed with

a. chlorine (group 17 of periodic table)

b. oxygen (group 16 of periodic table)

Answer :

1. Carbon (C) exhibits tetravalency and form four covalent bonds with other elements. Chlorine atom contain 7 valence electrons and forms one covalent bond with other elements. The compound that is formed by combination of carbon and chlorine is carbon tetrachloride.
2. Oxygen can form two covalent bonds and form carbon dioxide with carbon atom. The center carbon atom is bonded with two oxygen atoms through double covalent bonds. Hence the structure of carbon dioxide would be O=C=O.

41. In electron dot structure, the valence shell electrons are represented by crosses or dots.

a. The atomic number of chlorine is 17. Write its electronic configuration.

b. Draw the electron dot structure of chloride molecule.

Answer :

1. Atomic number of chlorine atom is 17. Hence the electronic configuration of Cl(17) would be;

K L M

2 8 7

2. Chlorine molecule is formed by formation of single covalent bond between two chlorine atoms. The electron dot structure of chlorine molecule is:

42. Catenation is the ability of an atom to form bonds with other atoms of the same elements. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Answer :

Both carbon (C) and silicon (Si) are placed in 14^th group of the periodic table and have four valence electrons in their valence shell.

Both of them can form four covalent bonds with other elements and can also exhibit the phenomenon of catenation.

Catenation is the self linkage property of atoms due to which they can bond with other similar atoms to form long chain compounds. It depends on the bond energy of atoms.

Out of carbon and silicon, carbon exhibits catenation much more than silicon. This is because of smaller size of carbon and high bond energy of C-C bonds compare to Si-Si bonds. Hence carbon shows catenation to a greater extent than silicon.

43. Unsaturated hydrocarbons contain multiple bonds between the two c-atoms and show addition reaction. Give the test to distinguish ethane from ethene.

Answer :

Ethene is an unsaturated hydrocarbon as it contains a double covalent bond between two carbon atoms. Presence of unsaturation or double covalent bond can be distinguished with the help of bromine solution in CCl4. It is an orange colour solution which shows colour change after addition in ethene solution.

The orange colour disappears because of formation of the colourless ethylene dibromide (CH2Br – CH2Br). It is an addition reaction of ethene due to presence of double covalent bond in the molecule.

CH2 = CH2 + Br à CH2Br – CH2Br

Ethane is a saturated hydrocarbon and cannot show this test. It burns with a clear flame whereas unsaturated hydrocarbons burn with yellow flame and lots of black smoke.

44. Match the reactions given in Column I with the name given in Column II.

Answer :

The matching of Column I and Column II is as given

45. Write the structural formulae of all the isomers of hexane.

Answer :

Hexane can exhibit five isomers with molecular formula C6H14.

46. What is the role of metal or reagents written on arrows in the given chemical reactions?

Answer :

1. Given reaction represents the hydrogenation of alkene which converts alkene to alkane by addition of hydrogen atoms to the carbon atoms included in double bond. Thus, nickel(Ni) here acts as the catalyst for hydrogenation reaction.
2. It is the esterification reaction between carboxylic acid and alcohol that forms ester and water molecules. Here concentrated sulphuric acid acts as catalyst as well as dehydrating agent. It provides hydrogen ions to initiate the reaction and also absorbs water molecules so that reaction can form more products.
3. This reaction involves the conversion of alcohol (ethanol) to carboxylic acid (acetic acid). It is an oxidation reaction and alkaline KmnO4 acts as an oxidising agent for ethanol.

Part C : Long Answer Type

47. A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write the chemical equation of the reaction involved.

Answer :

Ethanoic (CH3COOH) acid reacts with sodium hydrogen carbonate (NAHCO3) to form sodium ethanoate(CH3COONa), water and carbon dioxide gas. Hence salt X is sodium ethanoate and the gas evolved is CO2. The chemical equation of the reaction involved is:

CH3COOH + NaHCO3 à CH3COONa + H2O + CO2

Activity for observing the gas evolved in above reaction:

Set up the apparatus and take sodium hydrogen carbonate in test tube. Add ethanoic acid to it and observe brisk effervescence of carbon dioxide (CO2) gas. Now pass this gas through freshly prepared lime water (Ca(OH)2). It will turn milky due to the formation of insoluble calcium carbonate (CaCO3).

Ca(oh)2 + CO2 à CaCO3 + H2O

(milky)

48. a. What are hydrocarbons? Give examples.

b. Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.

c. What is functional group? Give examples of four different functional groups.

Answer :

1. Compounds which are formed from carbon and hydrogen atoms are called as hydrocarbons. Some common examples of hydrocarbons are methane, ethane, ethene, ethyne, cyclohexane and benzene.
2. Saturated hydrocarbons have only C-C bonds means all carbon atoms are bonded with single covalent bonds. The unsaturated hydrocarbons have multiple bonds between carbon atoms.
3. An atom or group of atoms that is responsible for characteristics physical and chemical properties for organic compound is found is called as functional group.

Examples of four functional groups are

49. Name the reaction which is commonly used in the conversion of vegetable oils of fats. Explain the reaction involved in detail.

Answer :

The reaction that is used to convert vegetable oil to fat is called as hydrogenation reaction. vegetable oils contain unsaturated hydrocarbons which can exhibit addition reaction with hydrogen to form saturated hydrocarbons or fats. The reaction occurs in the presence of metal catalyst like finely divided nickel or palladium at 200C and forms saturated vegetable fats.

The hydrogenation reaction is an industrial method for the manufacturing of vanaspati ghee from vegetable oil.

Here, R is any alkyl group which usually contains a large number of carbon atoms in vegetable oils.

50. a. Write the formula and draw electron dot structure of carbon tetrachloride.

b. What is saponification? Write the reaction involved in this process.

Answer :

1. The molecular formula of carbon tetrachloride is CCl4 and electron dot structure is as below.
2. Alkaline hydrolysis of an ester in the presence of a strong base like sodium hydroxide is called as saponification. It results the formation of corresponding salts of carboxylic acids and alcohol.

51. Esters are sweet smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labelled diagram.

Answer :

Take a test tube and add 1ml ethanol and 1 ml glacial acetic acid with a few drops of concentrated sulphuric acid. Now heat the solution in water bath for at least five minutes. Pour the content into a beaker containing water and smell the mixture. Sweet smell of ester would be observed.

Reaction of ethanoic acid and ethanol in the presence of concentrated sulphuric acid forms ethyl ethanoate with water.

CH3COOH + CH3CH2OH à CH3COOC2H5 + H2O

52. Draw the possible isomers of the compound with molecular formula C3H6O and also give their electron dot structures.

Answer :

Five isomers possible for the molecular formula C3H6O are listed below:

Chapter 5 : Periodic Classification of Elements

Part A : Multiple Choice Questions

1.Upto which element, the law of octaves was found to be applicable?

a.Oxygen

b.Calcium

c.Cobalt

d.Potassium

Answer : b

Explanation :

Newlands’ law of octaves could be applicable for elements having low atomic masses upto 40 u.

2.According to Mendeleev’s periodic law, the elements were arranged in the periodic table in the order of

a.Increasing atomic number

b.Decreasing atomic number

c.Increasing atomic masses

d.Decreasing atomic masses

Answer : c

Explanation :

The Mendeleev’s periodic law is an arrangement of elements in increasing order of their atomic masses as Mendeleev’s periodic law states that, the physical and chemical properties of elements are a periodic function of their atomic masses.

3.In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later?

a.Germanium

b.Chlorine

c.Oxygen

d.Silicon

Answer: a

Explanation :

Germanium element found a place in the periodic table later in the place of Eka-silicon in Mendeleev’s periodic table.

4.Which of the following statement about the modern periodic table are incorrect?

(i) The elements in the modern periodic table are arranged on the basis of their decreasing atomic numbers.

(ii) The elements in the modern periodic table are arranged on the basis of their increasing atomic masses.

(iii)Isotopes are placed in adjoining group(s) in the periodic table.

(iv)The elements in the modern periodic table are arranged on the basis of their increasing atomic number.

1. 1. 1. 1. 1. 1. 1. 5. Only (i)
                     6. (i),(ii) and (iii)
                     7. (i),(ii) and (iv)
                     8. Only (iv)

Answer : b

Explanation :

The modern periodic table is tabular arrangement of elements in increasing order of their atomic number therefore isotopes are placed at same position.

5.Which of the following statements about the modern periodic table is correct?

a.It has 18 horizontal rows known as periods.

b.It has 7 vertical columns rows known as periods.

c.It has 18 vertical columns known as groups.

d.It has 7 horizontal rows known as groups.

Answer : c

Explanation :

There are 18 vertical columns, known as groups and 7 horizontal rows in Modern periodic table.

6.Which of the given elements A, B, C, D and E with atomic number 2,3,7,10 and 30 respectively belong to the same period?

a. A,B,C

b. B,C,D

c. A,D,E

d. B,D,E

Answer : b

Explanation :

Second period of Modern Periodic Table contains elements from atomic number 3 to 10.

7.The elements A, B, C, D and E have atomic number 9,11, 17, 12 and 13 respectively. Which pair of elements belongs to the same group?

a. A and B

b. B and D

c. A and C

d. D and E

Answer : c

Explanation :

Elements having the same number of valence electrons belong to the same group.

Given elements and their electronic configurations are written below:

As, both A and C elements have the same number of valence electrons which is 7, hence they belong to the same group, i.e. 17^th group of periodic table.

8.Where would you locate the element with electronic configuration, 2, 8 in the modern periodic table?

a. Group 8

b. Group 2

c. Group 18

d. Group 10

Answer : c

Explanation :

Element with electronic configuration 2, 8 has octet configuration so must be an inter gas which is placed in group 18.

9.An element which is an essential constituent of all organic compounds belong to

a.Group 1

b.Group 14

c.Group 15

d.Group 16

Answer : b

Explanation :

Carbon is an essential element for all organic compounds and belong to group 14.

10. Which of the following is the outermost shell for elements of period 2?

a. K shell

b. L shell

c. M shell

d. N shell

Answer : b

Explanation :

The elements of 2^nd period contain two shells; K and L shell.

11.Which one of the following elements exhibit maximum number of valency electrons?

a. Na

b. Al

c. Si

d. P

Answer : d

Explanation :

As the group number increases, number of valence electrons also increases.

12. Which of the following gives the correct increasing order of the atomic radii of O, F and N ?

a. O,F,N

b. N,F,O

c. O,N,F

d. F,O,N

Answer : d

Explanation :

From left to right in the modern periodic table, the atomic radii decrease with increasing the atomic number. The atomic number of F, O and N are 9, 8 and 7 respectively so atomic radius will decrease from N to F.

13. Which among the following elements has the largest atomic radii?

a. Na

b. Mg

c. K

d. Ca

Answer : c

Explanation :

Na and Mg belong to same period whereas Na and K are in the same group. I a group from top to bottom, atomic radius increase whereas it decreases in period from left to right. Hence the order would be K> Na> Mg and K> Ca>Mg.

14.Which of the following elements would lose an electron easily?

a. Mg

b. Na

c. K

d. Ca

Answer : c

Explanation :

Na and K are alkali metals whereas Mg and Ca are alkaline earth metals. Alkali metals are model electropositive compare to alkaline earth metals and can easily lose electrons. Out of Na and K, K will easily lose electrons because of bigger size and less electronic attraction.

15.Which of the following elements does not lose an electron easily?

a. Na

b. F

c. Mg

d. Al

Answer : b

Explanation :

Metals can easily lose electrons and exhibit electropositive nature whereas non-metals have tendency to accept electrons and exhibit electronegative nature. Na, Al and Mg are metals whereas F is a non-metal.

16.Which of the following are the characteristics of isotopes of an element?

(i) Isotopes of an element have same atomic masses.

(ii) Isotopes of an element have same atomic number.

(iii)Isotopes of an element show same physical properties.

(iv)Isotopes of an element show same chemical properties.

1. 1. 1. 1. 5. (i), (iii) and (iv)
            6. (ii), (iii) and (iv)
            7. (ii) and (iii)
            8. (ii) and (iv)

Answer : d

Explanation :

Isotopes are the atoms of the same element which have same atomic number but different number of neutrons hence their atomic masses are different.

17.Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al.

a. Cl > Si > Al > Mg > Na

b. Na > Mg > Al > Si > Cl

c. Na > Al > Mg > Cl > Si

d. Al > Na > Si > Ca > Mg

Answer : b

Explanation :

As we move from left to right in periodic table, metallic characters decreases and non-metallic characters increases. Here Na, Si, Cl, Mg, Al belong to same period so we have to check their position in period.

18.Arrange the following elements in the order of their increasing non-metallic character Li, O, C, Be, F.

a. F < O < C < Be < Li

b. Li < Be < C < O < F

c. F < O < C < Be < Li

d. F < O < Be < C < Li

Answer : b

Explanation :

These all elements belong to same period in which non-metallic characters increases from left to right.

19.What type of oxide would Eka-aluminium form?

a.EO₃

b.E₃O₂

c.E₂O₃

d.EO

Answer : c

Explanation :

Eka-aluminium was later identified as Gallium with valency of 3. Hence the oxide would be E₂O₃.

20. Three elements B, Si and Ge are

a. Metals

b. Non-metals

c.Metalloids

d.Metals, non-metal and metalloid respectively

Answer : c

Explanation :

The elements boron (B), silicon (Si) and germanium (Ge) exhibit intermediate properties of metals and non-metals therefore they are called as metalloids. These elements are placed in between metals and non-metals as zigzag line to separate them.

21. Which of the following elements will form an acidic oxide?

a. An element with atomic number 7

b. An element with atomic number 3

c. An element with atomic number 12

d. An element with atomic number 19

Answer : a

Explanation :

Formation of acidic oxides is character of non-metals. Here elements with atomic number 7 is non-metal that is nitrogen. Results of all are metals.

22. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?

a. Metal

b. Mettaloid

c. Non-metal

d. Left-hand side element

Answer : b

Explanation :

Atomic number 14 is for Silicon element which is a metalloid and exhibit properties of both metals and non-metals. It has 4 electrons in its valence shell so tends to form covalent acidic oxide like non-metals.

23. Which one of the following depict the correct representation of atomic radius (r) of an atom?

a.(i) and (ii)

b.(ii) and (iii)

c.(iii) and (iv)

d.(i) and (iv)

Answer : b

Explanation :

The distance between the centre of the nucleus and the outermost shell known as atomic radius.

24.Which one of the following does not increase while moving down to group of the periodic table?

a. Atomic radius

b.Metallic character

c.Valence

d.Number of shells in an element

Answer : c

Explanation :

Elements of the same group have same number of valence electrons hence valency will remain same.

25.On moving from left to right in a period in the periodic table, the size of the atom

a. Increases

b. Decreases

c. Does not change appreciably

d. First decreases and then increases

Answer: b

Explanation :

As we move from left to right in the period of periodic table, the number of shell remains same but atomic number increases. So the electronic attraction over valence electrons also increases that decreases the atomic radius.

26.Which of the following set of elements is written in order of their increasing metallic character?

a. Be, Mg, Ca

b. Na, Li, K

c. Mg, Al, Si

d. C, O, N

Answer : a

Explanation :

As we move down in a group, metallic nature increases. Be, Mg and Ca belong to same group that is group 2 of Modern Periodic Table.

Part B : Short Answer Type

27. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of element called as? Give one example of such a set of elements.

Answer:

This is an example of Dobereiner’s traids which is a group of three elements. In Dobereiner’s traids the atomic masses of elements are arranged in such a way that the atomic mass of middle element is almost the mean of atomic masses of first and third elements.

For eg: Ca, Sr and Ba is one of the Dobereiner’s triads. Here, atomic masses of Ca, Sr and Ba are 40, 88 and 137 respectively. Atomic mass of Sr that is 88 is almost the mean of atomic masses of Ca and Ba.

Atomic mass of Sr = 40 +137 = 88.5

2

28.Elements have been arranged in the following sequence on the basis of their increasing atomic masses.

F, Na, Mg, Al, Si, P, S, Cl, Ar, K

a.Pick two sets of elements which have similar properties.

b.The given sequence represents which law of classification of elements?

Answer:

a.In this sequence, the elements are arranged in increasing order of their atomic masses. According to Newlands’ law of octaves, every eighth element will show similar properties as that of the first element. Hence F and Cl, Na and K will show similar properties.

Therefore, Set I is F and Cl.

And, Set II is Na and K.

b.In the given sequence, elements are arranged in increasing order of their atomic masses and each 8^th element shows similar properties. So, it represents the Newland law of law of octaves.

29. Can the following groups of elements be classified as Dobereiner’s triad?

a.Na, Si, Cl

b.Be, Mg, Ca

Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40

Explain by giving reason.

Answer:

For a group to be Dobereiner’s triad, the atomic mass of middle element must be average of atomic masses of the first and the third elements.

30.In Mendeleev’s periodic table, the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel having an atomic mass of 58.71 amu. Give reason for the same.

Answer :

In Mendeleev’s periodic table, the reasons for placing cobalt (Co) before nickel (Ni) though its atomic mass is higher than that of nickel, are:

1. Cobalt was placed in the group of rhodium(Rh) and iridium(Ir) because it exhibits the properties similar to them.
2. Similarly Nickel was placed with elements like palladium(Pd) and platinum(Pt) having properties similar to it.

31.’Hydrogen occupies a unique position in modern periodic table’, justify the statement.

Answer:

The position of hydrogen is unique in Modern Periodic Table. This is because:

1. The valence shell configuration of hydrogen and alkali metals is same, contain one electron. That is the reason, some of the properties of hydrogen are similar to those of alkali metals and it must be placed group 1.
2. Both hydrogen and halogens require one electron to complete their valence configuration therefore they show similarities in their properties and hydrogen can be placed in group 17.
3. Hydrogen also exhibits some unique properties like oxides of hydrogen (water) is neutral in nature whereas meals form basic oxides and halogens form acidic oxides.

32.Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.

Answer:

Eka-silicon is identified as germanium(Ge) which is placed in group 4 of Mendeleev’s periodic table. The valency of germanium is 4 so the chemical formula for chloride must be GeCl₄.

Eka-aluminium was later identified as gallium (Ga). It is placed in group 3 of the Mendeleev’s periodic table. Hence the valence of gallium is 3 and the formula of chloride would be GaCl3.

33.Three elements A, B and C have 3, 4 and 2 electrons respectively in their outermost shell. Give the group number to which they belong in the modern periodic table. Also, give their valencies.

Answer:

The group number for elements can be identified as 10+ number of valence electrons Element A with 3 valence electrons must show valency as 3 and should belongs to group 13. The elements of group 13 are B, Al, Ga, In or TI.

Element B contains 4 valence electrons so it must be from group 14 (10+4) and valency should be 4. The element B can be C, Si, Ge, Sn or Pb. Similarly Element C has two valence electrons hence must be from group 2. So element C can be Be, Mg, Ca, Sr, Ba or Ra.

34.If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride?

Answer :

Elements of group 14 have 4 valence electrons and valency would be 4. Group 14 contains metals and non-metals with metalloids.

As there are four valence electrons so it must involve in covalent bonding to complete its octet configuration. So the chemical formula of chloride of element X would be XCl₄.

Since chloride is formed by sharing of electrons therefore the nature of the chloride of element X will be covalent.

35.Compare the radii of two species X and Y. Give reasons for your answer.

a.X has 12 protons and 12 electrons.

b.Y has 12 protons and 10 electrons

Answer:

Here X has same number of electrons and protons, therefore it is a neural atom whereas Y contains 12 protons and 10 electrons so there are 2 protons extra giving Y charge of +2. The electronic configurations of the two species can be expressed as:

The atomic size of a cation is always smaller than a neutral atom containing same number of protons this is because cation has less number of electrons due to which the nuclear attractions are more on electrons in cation causing its size to be smaller than that of the neutral atom.

Hence, atomic radius of Y is smaller than that of X.

36. Arrange the following elements in increasing order of their atomic radii

a. Li, Be, F, N

b. Cl, At, Br, I

Answer :

a.Li, Be, F and N belong to same period of modern periodic table. As we move left to right in the periodic table, the atomic radii of elements decreases due to high atomic charge and same number of shell. Thus the atomic radii of Li, Be, F and N increase in the order : F < N < Be < Li.

b.Cl, At, Br and I belong to some group of periodic table that is group 17. As we move down in a group, the atomic radii of elements increase due to increasing the number of shell. Thus, atomic radii of Cl, At, Br and I increase in the order : Cl < Br< I < At.

37.Identify and name the metals out of the following elements whose electronic configurations are given below.

a. 2, 8, 2

b. 2, 8, 1

c. 2, 8, 7

d. 2, 1

Answer:

Elements with having 1 to 3 valence electrons are usually metals whereas elements with 4 or more valence electrons are usually non-metals or metalloids.

Therefore, from given electronic configurations, metals are:

a.2,8,2 – Magnesium(12)

b.2, 8,1 -Sodium (11)

c.2,1 – Lithium(3)

38. Write the formula of the product formed when the element A (atomic number 19) combines with the element B (atomic number 17). Draw its electronic dot structure. What is the nature of the brand formed?

Answer :

The electronic configuration of element A with atomic number 19 would be 2, 8,8,1. Hence it is potassium. Since, it has only one valence electron therefore it must be a metal.

The electronic configuration of element B would be 2, 8, 7 with number of valence electrons being 7. So, it must be a non-metal that is chlorine.

A metal and a non-metal usually combine through ionic bond because metals have tendency to lose electrons and form cations whereas non-metals can accept electrons to form anions.

Potassium and chlorine will form potassium chloride(KCl).

The electron dot structure of KCl is as given below.

39.Arrange the following elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga.

Answer:

The arrangement of given elements in the Modern Periodic table is listed below.

We know that metallic character decreases from left to right in the periodic table. In the given elements, excluding Mg, remaining elements are placed in same period so the metallic character will decrease from K to Ge and order of metallic character would be;

Ge < Ga < Ca < K

Now, as we move down in a group, metallic nature of elements increases. So, Ca is more metallic than Mg. Similarly, Mg will be less metallic than K because in period, metallic nature decreases from left to right. Hence the increasing order of metallic character would be;

Ge < Ga < Mg < Ca < K

40.Identify the elements with the following property and arrange them in increasing order of their reactivity.

a.An element which is a soft and reactive metal.

b.The metal which is an important constituent of limestone.

c.The metal which exists in liquid state at room temperature.

Answer:

a.Alkali metals like sodium and potassium are soft and reactive.

b.The chemical formula of limestone is CaCO₃ hence the important constituent of limestone would be calcium (Ca).

c.Mercury is the only metal which exists in liquid state at room temperature.

Since reactivity of metals decreases from left to right in the group therefore the order of reactivity of Na, Ca and Hg would be;

Hg < Ca < Na

41.Properties of the elements are given below. Where would you locate following elements in the periodic table?

a. A soft metal stored under kerosene.

b.An element with variable (more than one) valency stored under water.

c.An element which is tetravalent and forms the basis of organic chemistry.

d.An element which is an inert gas with atomic number 2.

e.An element whose thin oxide layer is used to make other elements corrosion resistant by the process of “anodising”.

Answer :

a.Because of high reactivity of alkali metals, they are usually kept under kerosene. Alkali metals are placed in group 1 and starts from period 2 to 7.

b.The element with variable valency and must be stored in water is phosphorus. It shows variable valency of 3 and 5 and is reactive towards air and not water. It is placed in group 15 and period 3 of periodic table.

c. Carbon forms the basis of organic compounds. It exhibits tetra-valency because it has 4 valance electrons. It is placed in group 14 and period 2 of Periodic table.

d. Helium is the lightest inert gas with atomic number 2. It is placed in group 18 and period 1 of periodic table.

e. Aluminium metal is used to make other elements corrosion resistant by the process of “anodising”. The oxide layer is of Al₂O₃. The atomic number of aluminium is 13 and it is placed in group 13 and period 3 of periodic table.

Part C : Long Answer Type

42. An element is placed in 2^nd group and 3^rd period of the periodic table burns in presence of oxygen to form a basic oxide.

a. Identify the element

b. Write the electronic configuration

c. Write a balanced equation when it burns in the presence of air.

d. Write a balanced equation when this oxide is dissolved in water.

e. Draw the electron dot structure for the formation of this oxide.

Answer:

a.Given element is placed in group 2 so it must be alkaline earth metal. The alkaline earth metal in period 3 in magnesium (Mg).

b.The atomic number of Mg is 12, and electronic configuration is:

K L M

2 8 2

c.Magnesium burns in the presence of air to form magnesium oxide(MgO). It is a basic oxide.

2Mg(s) + O₂(g)à 2MgO(s)

d.Basic oxide of magnesium; MgO is dissolved in water to form magnesium hydroxide.

2MgO(s) + 2H₂O (I) à 2Mg(OH)₂ (aq)

e.Magnesium oxide is an ionic compound in which Mg exists as Mg⁺² ion and oxygen as O^-2 ion. The electron dot structure for the formation of magnesium oxide is given below.

43. An element X (atomic number 17) reacts with an element Y (atomic number 20) to form a divalent halide.

a. Where in the periodic table are elements X and Y placed?

b. Classify X and Y as metal (s), non-metal(s) or metalloid(s).

c.What will be the nature of oxide of element Y? Identify the nature of bonding in the compound formed.

d.Draw the electron dot structure of the divalent halide.

Answer:

a.The atomic number of element X is 17 and electronic configuration 2, 8, 7. There are 7 valence electrons so it must be placed in group 17 and period 3. It is chlorine. The atomic number of Y is 20 and electronic configuration is 2, 8, 8, 2. So there are 2 valence electrons and it must be a part of group 2^nd and 4^th period as there are four shells. The element Y is calcium.

b.Chlorine (element X) has 7 valence electrons hence it requires one electron to get the octet configuration. So it has tendency to accept one electron and form anion. Therefore it is a non-metal. Element Y has two valence electrons which can easily lose to get the stable electronic configuration of the nearest inert gas. Hence it is a metal.

c.Calcium is a metal and it will form basic oxides like calcium oxide(CaO) must be basic in nature. Here calcium is metal and oxygen is non-metal therefore the bonding between metals and non-metals must be ionic in nature.

d.The chemical formula of divalent halide of calcium and chlorine would be CaCl₂. Electron dot structure for the formation of calcium chloride is given below.

44. Atomic number of a few elements are given below.

10, 20, 7, 14

a.Identify the elements.

b.Identify the group number of these elements in the periodic table.

c.Identify the periods of these elements in the periodic table.

d.What would be the electronic configuration for each of these elements?

e.Determine the valency of these elements.

Answer:

45.Complete the following crossword puzzle(figure).

Across

1.An element with atomic number 12.

3.Metal used in making cans and member of group 14.

4.A lustrous non-metal which has 7 electrons in its outermost shell.

Down

2.Highly reactive and soft metal which imparts yellow colour when subjected to flame and is kept in kerosene.

5.The first element of second period.

6.An element which is used in making florescent bulbs and is second member of group 18 in the modern periodic table.

7. A radioactive element which is the last member of halogen family.

8.Metal which is an important constituent of steel and forms rust when exposed to moist air.

9.The first metalloid in modern periodic table whose fibres are used in making bullet-proof vests.

Answer :

Across

1.Magnesium

3.Tin

4.Iodine

Down

2.Sodium

5.Lithium

6.Neon

7.Astatine

8.Iron

9.Boron

46. a. In this ladder(figure) symbols of elements are jumbled up. Rearrange these symbols of elements in the increasing order of their atomic numbers in the periodic table.

b. Arrange them in the order of their group also

Answer:

a.The symbols of elements in increasing order of their atomic numbers are:

H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca.

b.The symbols of elements in increasing order of their group numbers are as follows.

47. Mendeleev predicted the existence of certain elements not known at that time and named two of them as Eka-silicon and Eka-aluminium.

a. Name the elements which have taken the place of these elements.

b.Mention the group and the period of these elements in the modern periodic table.

c. Classify these elements as metals, non-metals or metalloids.

d.How many valence electrons are present in each one of them?

Answer:

a.Eka-silicon was later identified as Germanium (Ge) and Eka-aluminium was taken as Gallium (Ga).

b. Germanium (Ge) – Group 14, period 4

Gallium (Ga) – Group 13, period 4

c.Gallium is a metal while Germanium is a metalloid.

d.Gallium is placed in 13^th group so there must be 13-10=3 valence electrons.

Similarly germanium is placed in group 14 so there must be 14-10=4 valence electrons.

48. a.Electropositive nature of the element increases down the group and decreases across the period.

b.Electronegativity of the element decreases down the group and increases across the period.

c.Atomic size increases down the group and decreases across a period(left to right).

d.Metallic character increases down the group and decreases across a period.

On the basis of the above trends of the periodic table, answer the following about the elements with atomic number 3 to 9.

a.Name the most electropositive element among them.

b.Name the most electronegative element.

c.Name of the element with smallest atomic size.

d.Name the element which is a metalloid.

e.Name the element which shows maximum valency.

Answer:

Elements from atomic number 3 to 9 are listed below:

a.Most electropositive element – Lithium(Li)

b.Most electronegative element – Fluorine

c. Element with smallest atomic size – Fluorine

d. Metalloid element – Boron

e. Element with maximum valency – Carbon

49.Which group of elements could be placed in Mendeleev’s periodic table without disturbing the original order? Give reasons.

Answer :

Since noble gases are inert due to completely filled octet configuration. Therefore, the presence cannot affect the existing order of any group of periodic table.

These nobel gases are present in extremely low concentrations in our atmosphere and usually do not form any chemical compound with other elements.

During the development of periodic table by Mendeleev, these gases were not known. That is the reason, after their discovery they were placed in a new group at the right most end of periodic table and named as zero group or 18^th group.

50. Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “periodic law”?

Answer :

Mendeleev purposed the relation between atomic masses of elements and their properties. He examined that physical and chemical properties of elements are period function of their atomic masses. He arranged all known 63 elements according to their atomic masses.

He examined the compounds formed by elements hydrogen and oxygen. He used these elements because they readily form different compounds with other elements like hydride and oxides.

The chemical properties of hydrides and oxides were used to determine the chemical properties of different elements and that again used for their classification. He recorded properties of all 63 elements and paired the elements which exhibit same chemical properties. Later he arranged elements on the basis of their similarities in chemical properties and found that most of the elements were arranged in order of their increasing atomic masses.

In this arrangement, he also observed the periodic recurrence of elements with similar physical and chemical properties. He formulated the periodic law which states that the properties of elements are the periodic functions of their atomic masses.

Chapter 6 : Life processes

Part A : Multiple Choice Questions

1.Which of the following statements about the autotrophs is incorrect?

a. They synthesize carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll.

b. They store carbohydrates in the form of starch.

c. They convert carbon dioxide and water into carbohydrates in the absence of sunlight.

d. They constitute the first trophic level in food chains.

Answer: c

Explanation:

Autotrophs obtain the required carbon and energy requirements from carbon dioxide and sunlight. They combine carbon dioxide and water to form carbohydrates. The main photosynthetic pigment is chlorophyll, which helps to trap the sunlight to carry out the light reaction of photosynthesis to synthesise carbohydrates. Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupy first trophic level in food chain and serve as a source of food and energy for organisms of higher trophic levels.

2.In which of the following groups of organisms, food material is broken down outside the body and absorbed?

a. Mushroom, green plants, Amoeba

b. Yeast, mushroom, bread mould

c. Paramecium, Amoeba, Cuscuta

d. Cuscuta, lice, tapeworm

Answer : b

Explanation :

Yeast, mushroom and bread mould are saprophyte which derive their nutrition from dead organisms. For the purpose, these organisms secrete digestive enzymes on their substratum to break down the complex food material into the simpler ones. These digested food materials are then absorbed by them.

3.Select the correct statement.

a. Heterotrophs do not synthesize their own food.

b. Heterotrophs utilize solar energy for photosynthesis.

c. Heterotrophs synthesize their own food.

d. Heterotrophs are capable of converting carbon dioxide and water carbohydrates.

Answer : a

Explanation :

Heterotrophs are the organisms that cannot synthesize their own food and depend on available organic or inorganic compounds to fulfil their energy requirements. Eg. All animals.

4. Which is the correct sequence of parts in human alimentary canal?

a. Mouth à Stomach à Small intestine à Oesophagus àLarge intestine

b. Mouth à Oesophagusà Stomach à Large intestineà Small intestine

c. Mouth à Stomach à Oesophagusà Small intestineàLarge intestine

d. Mouth à Oesophagusà Stomach Small intestineàLarge intestine

Answer : d

Explanation :

Human alimentary canal consists of organ of digestion which are namely, in sequence, mouth, oesophagus, stomach, small intestine, large intestine and anus.

5. If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected?

a. Proteins breaking down into amino acids

b. Starch breaking down into sugars

c. Fats breaking down into fatty acids and glycerol

d. Absorption of vitamins

Answer : b

Explanation:

Amylase is the enzyme which helps in primary digestion of starch only. Digestion of starch by salivary amylase into maltose starts in mouth. Oesophagus then pushes the food into stomach. It does not carry out digestion at all. Pancreatic amylase also digests remaining starch into maltose sugars. Intestinal maltase carries out final chemical digestion of maltose into glucose molecules.

6. The inner lining of stomach is protected by one of the following from hydrochloric acid. Choose the correct one.

a. Pepsin

b. Mucus

c. Salivary amylase

d. Bile

Answer : b

Explanation :

The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus. HCl impart highly acidic pH to stomach which help in the further digestion of food. The mucus in gastric juice helps protect the stomach wall from corrosive effect of hydrochloric acid.

7. Which part of alimentary canal receives bile from the liver?

a. Stomach

b. Small intestine

c. Large intestine

d. Oesophagus

Answer : b

Explanation :

Bile is secreted by liver and is stored in gall bladder from where it enters the small intestine via common duct.

8. A few drops of iodine solution were added to rice water. The solution were added to rice water. The solution turned blue-black in colour. This indicates that rice water contains

a. Complex proteins

b. Simple proteins

c. Fats

d. Starch

Answer : d

Explanation :

Presence of starch in a solution turns added iodine drops in blue black color. Hence, the blue-black colour of rice water confirms presence of starch.

9. In which part of the alimentary canal food is finally digested?

a.Stomach

b.Mouth cavity

c.Large intestine

d.Small intestine

Answer : d

Explanation :

Digestion of food starts in mouth by salivary amylase. From here it enters into the stomach via oesophagus. Gastric juice of stomach digests the protein part of food. Pancreatic amylase, trypsin and lipase as well as intestinal peptidases and maltase carry out the final chemical digestion of food in small intestine. The simpler substances formed by chemical digestion are then absorbed by small intestinal villi.

10. Choose the function of the pancreatic juice from the following

a. Trypsin digests proteins and lipase carbohydrates

b. Trypsin digests emulsified fats and lipase proteins

c. Trypsin and lipase digest fats

d. Trypsin digests proteins and lipase digests emulsified fats droplets

Answer : d

Explanation :

Pancreatic juice contains sodium bicarbonate and digestive enzymes amylase, trypsin, lipase and nucleases. Pancreatic amylase carries out digestion of starch, trypsin digests protein, and lipase breaks down fat droplets already emulsified by bile salts.

11. When air is blown from mouth into a test-tube containing lime water, the lime water turned milky due to the presence of

a. Oxygen

b. Carbon dioxide

c. Nitrogen

d. Water vapour

Answer: b

Explanation :

Carbon dioxide gas turns lime water milky. Since the exhaled air is carbon dioxide rich, when air is blown from mouth into test tube, the lime water turned milky.

12. Which of the following statements are true about respiration?

I. During inhalation, ribs move inward and diaphragm is raised.

II. In the alveoli, exchange of gases takes place, i.e., oxygen form alveolar air diffuses into blood and carbon dioxide from blood into alveolar air.

III. Haemoglobin has greater affinity for carbon dioxide than oxygen.

IV. Alveoli increases surface area for exchange of gases.

a.I and IV

b.II and III

c.I and III

d.II and IV

Answer: d

Explanation :

During inhalation, diaphragm contracts and lowers while the rib cage moves upward and outward.

13. Which is the correct sequence of air passage during inhalation?

a. Nostrils à Larynx Pharynx à Trachea à Lungs

b. Nasal passage à Trachea à Pharynx à Larynx à Alveoli

c. Larynx à Nostrils à Pharynx àLungs

d. Nostrils à Pharynxà Larynx à Trachea àAlveoli

Answer : d

Explanation :

During inhalation, the air is drawn through the nostrils into nasal passage. From there, air enters into pharynx, larynx, trachea, bronchi, lungs and finally to the alveoli.

14. During respiration exchange of gases take place in

a. Trachea and larynx

b. Alveoli of lungs

c. Alveoli and throat

d. Throat and larynx

Answer : b

Explanation :

An alveolar sac is made up of simple squamous epithelium and is surrounded by blood capillaries. Thin walls and increased surface area favor the gaseous exchange which takes place between the oxygen rich alveolar air and the carbon dioxide rich blood in the capillaries at alveolar surface. Oxygen diffuses across the alveolar and capillary walls to enter the bloodstream, while carbon dioxide diffuses from the blood across these walls to enter the alveoli.

15. Which of the following statements are true about heart?

I. Left atrium receives oxygenated blood from different parts of body while right atrium receives deoxygenated blood from lungs.

II. Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs.

III. Left atrium transfers oxygenated blood to right ventricle which sends it to different body parts.

IV. Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body.

a.I

b.II

c.II and IV

d.I and III

Answer: c

Explanation :

The left ventricle pumps blood into the aorta which in turn delivers it to the major body regions and organs which makes statement III incorrect. The anterior vena cava collects deoxygenated blood from the head, chest and arms and enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both venae cavae pass the deoxygenated blood to the right atrium which makes statement I incorrect. Blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation, this makes statement II and IV correct.

16. What prevents backflow of blood inside the heart during contraction?

a. Valves in heart

b. Thich muscular walls of ventricles

c. Thin walls of atria

d. All of these

Answer : a

Explanation:

Valves ensure that blood does not flow backwards when the atria or ventricles contract. Semilunar valves, the valves present between ventricles and their attached vessels, serve to prevent the backflow of blood to ventricles from their respective attached vessels. Likewise, atrioventricular (AV) valve between atrium and ventricle directs the flow of blood and prevents any backflow into atria.

17. Single circulation, i.e blood flows through the heart only once during one cycle of passage through the body, is exhibited by

a. Labeo, chameleon, salamander

b. Hippocampus, exocoetus, anabas

c. Hyla, rana, draco

d. Whale, dolphin, turtle

Answer: b

Explanation :

The examples and the relation of animal group and heart are as fishes have two chambered heart and exhibit single circulation while three chambered heart of amphibian and reptiles and four chambered heart of birds and mammals exhibit double circulation. In given options, C includes all fishes which makes it correct answer.

18. In which of the following vertebrate groups, heart does not pump oxygenated blood to different parts of the body?

a. Pisces and amphibians

b. amphibians and reptiles

c. Amphibians only

d. Pisces only

Answer : d

Explanation :

Fishes have two chambered heart and exhibit single circulation wherein deoxygenated blood is pumped to gills. Gills are the organs of gaseous exchange by diffusion. The oxygenated blood from gills is then pumped to different body parts and the deoxygenated blood from body parts is then carried to heart. The three chambered heart of amphibian and reptiles and four chambered heart of birds and mammals exhibit double circulation and pump oxygenated blood to body.

19. Choose the correct statement that describes arteries.

a. They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart.

b. They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body.

c. They have thick elastic walls, blood flows under low pressure carry blood from the heart to various organs of the body.

d. They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.

Answer : d

Explanation :

Arteries are the valveless blood vessels which serve to transport the blood away from the heart to various body parts. The thick strong elastic walls of arteries withstand the high pressure of blood coming from heart.

20. The filtration units of kidneys are called

a. ureter

b. urethra

c. neurons

d. nephrons

Answer : d

Explanation :

Nephrons are the structural and functional filtration unit of a kidney that serve in filtration, reabsorption and secretion. Ureters are small muscular tubes that extend from the kidney and carry urine into the urinary bladder. The urethra is a canal that carries urine from bladder and expels it out of body. Neurons are structural and functional unit of nervous system.

21. Oxygen liberated during photosynthesis comes from

a. water

b. chlorophyll

c. carbon dioxide

d. glucose

Answer: a

Explanation :

Photosynthesis is the process wherein carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds (carbohydrates).

The main photosynthetic pigment chlorophyll and accessory pigments chl b, chl c and carotenoids etc trap the sunlight to carry out the light reactions of photosynthesis. The light reaction of photosynthesis includes splitting of water into oxygen and hydrogen to produce ATP and reducing agents which in turn serve as energy source to drive the second phase of photosynthesis during which carbohydrate synthesis takes place.

26. The blood leaving the tissues becomes richer in
    1. Carbon dioxide
    2. Water
    3. Hemoglobin
    4. Oxygen

Answer : a

Explanation :

The left ventricle pumps blood into the aorta which in turn branches and delivers oxygenated blood to the major body regions and organs. The oxygen is consumed in cellular respiration and the carbon dioxide produced during respiration enters into blood.

The anterior vena cava collects deoxygenated blood from the head, chest and arms enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both vena cava pass the deoxygenated blood to the right atrium. Thus, blood from tissues is rich in carbon dioxide.

Deoxygenated blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation.

23. Which of the following is an incorrect statement?

a. Organisms grow with time

b. Organisms must repair and maintain their structure

c. Movement of molecules does not take place among cells

d. Energy is essential for life processes.

Answer : c

Explanation :

A cell is structural and functional unit of a living organisms. Each cell is made up of molecules. Several chemical reactions related to life processes take place in cell and the molecules exhibit movement during these reactions. This makes options incorrect statement and correct answer.

The growth is key character of living organisms. Various chemical changes, biological reaction cause wear and tear or organelles and alter the organized structure of living organisms. The living organisms have to repair and maintain their structures using the energy produced by cellular respiration of food.

24. The internal (cellular) energy reserve in autotrophs is

a. Glycogen

b. Protein

c. Starch

d. Fatty acid

Answer : c

Explanation :

Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds. The main photosynthetic pigment chlorophyll a and accessory pigment chl b, chl c and carotenoids trap the sunlight to carry out the light reactions of photosynthesis. The light reaction of photosynthesis produces ATP and reducing agents which in turn serve as energy source to drive the second phase of photosynthesis during carbohydrate synthesis takes place.

The carbohydrates which are not immediately consumed by plants are store as starch(homopolysaccharide of D-glucose).

Glycogen serves as main stored form of carbohydrates in animals.

25.The opening and closing of the stomatal pore depends upon

a. Oxygen

b. Temperature

c. Water in guard cells

d. Concentration of CO 2 in stomata

Answer : c

Explanation :

Stomata are the tiny pores present at the leaf surface. Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells. When water flows in guard cells from epidermal cells, guard cells become turgid and stomata are opened. Removal of water from guard cells makes them flaccid and stomata are closed.

The only epidermal cells with unevenly thickened walls and chloroplasts are the guard cells; they are kidney shaped in dicots and dumbell shaped in monocots.

27. Choose the forms in which most plants absorb nitrogen

i.Proteins

ii.Nitrates and nitrites

iii.Urea

iv.Atmospheric nitrogen

1. 1. (i) and (ii)
   2. (ii) and (iii)
   3. (iii) and (iv)
   4. (i) and (iv)

Answer: None of these

Explanation:

Plants absorb nitrogen from the soil in the form of nitrate and ammonium. All other nitrogen sources must be broken down into either of these two forms to be absorbed by plants.

28. Which is the first enzyme to mix with food in the digestive tract?
    1. Pepsin
    2. Cellulase
    3. Amylase
    4. Trypsin

Answer: c

Explanation :

Chemical digestion of food starts in the mouth. Digestion of starch by salivary amylase takes place in mouth. Oesophagus serves to push the food into stomach only. No digestion takes place here. Gastric juice of stomach digests the protein part of food. Pancreatic amylase, trypsin and lipase as well as intestinal peptidases and maltase carry out chemical digestion of food in small intestine. The simpler substances formed by chemical digestion are then absorbed small intestinal villi. Large intestine is the organ of water and salts reabsorption from undigested food and elimination of remaining undigested material out of body. This makes option C correct answer.

29. Which of the following statements are correct?

i.Pyruvate can be converted into ethanol and carbon dioxide by yeast.

ii.Fermentation takes place in aerobic bacteria.

iii.Fermentation takes place in mitochondria.

iv.Fermentation is a form of anaerobic respiration.

1. 1. (i) and (iii)
   2. (ii) and (iv)
   3. (i) and (iv)
   4. (ii) and (iii)

Answer : c

Explanation :

Yeast is a unicellular organism which carries out ethanol fermentation. The first phase is break down of one molecule of glucose into two molecules of pyruvate which occurs in cytoplasm. Due to limited oxygen availability, pyruvate remains in cytoplasm where pyruvate decarboxylase and alcohol dehydrogenase enzymes carry out the second phase of anaerobic respiration and produce ethanol and carbon dioxide.

30. Lack of oxygen in muscles often leads to cramps among cricketers. This result due to
    1. Conversion of pyruvate to ethanol
    2. Conversion of pyruvate to glucose
    3. Non-conversion of glucose to pyruvate
    4. Conversion of pyruvate to lactic acid

Answer: d

Explanation :

Respiration is the sole source of energy in muscles. During intense physical activity, limited oxygen supply do not support the aerobic respiration and muscles carry out lactic acid fermentation of pyruvate to meet the energy demand.

31. During deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the
    1. Cytoplasm
    2. Chloroplast
    3. Mitochondria
    4. Golgi body

Answer: a

Explanation :

Pyruvic acid to lactic acid formation is an anaerobic process which occurs in cytoplasm only.

Part B : Short Answer Type

32. Name the following.
    1. The process in plants that links light energy with chemical energy.
    2. Organisms that can prepare their own food.
    3. The cell organelle where photosynthesis occurs.
    4. Cells that surround a stomatal pore.
    5. Organisms that cannot prepare their own food.
    6. An enzyme secreted from gastric glands in stomach that acts on proteins.

Answer :

a.Photosynthesis is the process wherein carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds ie. Conversion of light energy into chemical energy.

b.Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds.

c. Chloroplasts is a double membrane bound organelle that contain machinery for photosynthesis.

d. Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells.

e. Heterotrophs organisms that cannot make their own food from inorganic substances and depend on other organisms for their food.

f. Pepsin is a protein digestive enzyme.

33. All plants give out oxygen during day and carbon dioxide during night. Do you agree with this statement? Give reason.

Answer :

True. Respiration is the process of oxidation of food substances that release carbon dioxide; it takes place throughout the day. Photosynthesis is the process of fixing the atmospheric carbon dioxide into organic compounds with release of oxygen gas as by product. Photosynthesis takes place during day in presence of sunlight only. Hence, plants release oxygen during day only while carbon dioxide is released during night.

34. How do the guard cells regulate opening and closing of stomatal pores?

Answer :

Each stomatal pore is surrounded by two guard cells that assist in stomatal opening driven by turgidity of guard cells. The guard cells are the only epidermal cells with unevenly thickened walls and chloroplasts. When water flows in guard cells from epidermal cells, guard cells become turgid and stomata are opened. Loss of water from guard cells makes them flaccid and stomata are closed.

35. Two green plants are kept separately in oxygen free containers, one the dark and the other in continuous light. Which one will live longer? Give reasons.

Answer:

Respiration and photosynthesis are the two vital processes for plant life. The plant kept in light would be able to produce oxygen, required for respiration, by the process of photosynthesis and would live longer. The one kept in dark would die as soon as the container becomes filled with carbon dioxide gas produced by respiration.

36. If a plant is released carbon dioxide and taking oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer.

Answer :

Respiration is the process of oxidation of food substances that release carbon dioxide it takes places throughout the day. Photosynthesis is the process of fixing the atmospheric carbon dioxide into organic compounds with release of oxygen gas as by product. Photosynthesis takes place during day in presence of sunlight only.

The CO2 released during respiration is absorbed by plants for photosynthesis in day causing net released of oxygen only. If a plant is releasing carbon dioxide and taking in oxygen during the day, it means that either rate of photosynthesis is too slow to count balance the release CO2 by respiration or photosynthesis is not taking place at all.

37. Why do fishes die when taken out of water?

Answer :

Gills are the organ of gaseous exchange in fishes as they have two chambered heart and heart pump the deoxygenated blood to gills. Rich in blood capillaries, these gills serve as surface for exchange as CO2 and oxygen between deoxygenated blood and surrounding. As they are taken out of water, gills are no longer able to absorb oxygen causing its death.

38. Differentiate between an autotroph and a heterotroph.

Answer :

Autotrophs are the organisms that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds. Heterotrophs are the organisms that depend on available organic compounds and cannot carry out the photosynthesis.

Presence of photosynthetic pigment chlorophyll and carotenoids enable autotrophs to trap the sunlight to carry out the light reactions of photosynthesis. Heterotrophs lack these pigments.

Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupies first trophic level in food chain and serve as source of food and energy for organisms of higher trophic levels. Heterotrophs occupy the higher trophic level and function as consumers.

39. Is “nutrition” for an organism is for:

Need of nutrition for an organism is for:

1. 1. To serve as energy source for metabolic processes in the body.
   2. To support growth of new cells and repair and maintenance of existing cells.
   3. To provide resistance against various diseases.
2. What would happen if green plants disappear from earth?

Answer :

Green plants are autotrophs are that use light as source of energy, carbon dioxide as chief carbon source and water as electron donor to fix the atmospheric carbon dioxide into organic compounds. The carbohydrates which are not immediately consumed by plants are stored as starch.

Since autotrophs are the only organisms that can fix the atmospheric carbon dioxide into organic compounds, these organisms occupy first trophic level in food chain and serve as source of food and energy for all other organisms of higher trophic levels.

Hence in absence of these plants, whole functioning of whole ecosystem will come to hault due to lack of food and energy source for consumers (herbivores, carnivores and omnivores)

41. Leaves of a healthy potted plant were coated with vaseline. Will this plan remain healthy for long? Give reasons for your answer.

Answer:

Coating of vaseline will make the leaves impervious to gases and water. This will result in adverse impact on it because

1. 1. Plant will not be able to take in oxygen for respiration and carbon dioxide for photosynthesis.
   2. Since transpiration pull drive the upward movement of water and minerals in xylem water transport will be hampered.
2. How does aerobic respiration differ from anaerobic respiration?

Answer:

The aerobic respiration differ from anaerobic respiration is as

43. Match the words of column A with that of column B.

Answer:

Words of column A are matched with that of column B as below:

44. Differentiate between an artery and a vein.

Answer:

The differentiate between an artery and a vein are as below:

45. What are the adaptations of leaf for photosynthesis?

Answer :

Leaves shows following adaptions for photosynthesis

45. 1. Leaves serve to provide large surface area to facilitate maximum light absorption.
    2. The extensive network of veins helps quick transport of substances to and from the mesophyll cells.
    3. Leaves contain chloroplasts, the site for photosynthesis. Since upper surface of leaves are directly illuminated, number of chloroplast is higher in the upper surface.
    4. Presence of tiny pores called as stomata on leaf’s surface facilitate gaseous exchange and transpiration.
46. Why is small intestine in herbivores longer than in carnivores?

Answer :

Herbivores derive their nutrition from plants and plants product which in turn make cellulose main component of their diet. Since cellulose digestion is a long process and is done by intestinal ruminant bacteria present in gut of herbivores, complete digestion of cellulose need the food to stay for longer time in gut. Presence of longer intestine serves the purpose and allows the food to stay for longer duration to facilitate proper digestion of cellulose. Carnivores feed on herbivores and hence cellulose is not part of their diet which in turn causes no need of longer intestine.

47. What will happen if mucus is not secreted by the gastric glands?

Answer :

The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus. HCl impart highly acidic pH to stomach which in turn supports conversion of inactive pepsinogen into active pepsin.

Mucus plays an important role and protects the lining of stomach against erosion from hydrochloric acid produced in the stomach. In absence of mucus, HCl will cause erosion and ulcer in stomach lining.

47.What is the significance of emulsification of fats?

Answer:

Fats are large complex biomolecules present in form of large globules which in turn does not support enzymatic action on them.

Bile is secreted by liver and is stored in gall bladder. Ducts from the gallbladder and pancreas join to form common duct that enters the duodenum. The small intestine receives bile from the gall bladder via this common duct.

Bile salts carry out mechanical digestion of large fat globules into smaller ones which are then acted upon by intestinal lipase for complete digestion.

48.What causes movement of food inside the alimentary canal?

Answer :

Peristalsis is rhythmic contraction of muscular wall of alimentary canal which in turn pushes the food along the alimentary canal. Peristalsis begins in the esophagus and continues in all the organs of the alimentary canal.

49.Why does absorption of digested food occur mainly in the small intestine?

Answer:

Absorption of digested food occurs mainly in small intestine because:

1. 1. Chemical and mechanical digestion of food reaches to completion in small intestine.
   2. The fingerlike projection of mucosa into lumen of small intestine as called as villi which in turn serve to increase the surface area to facilitate maximum absorption of digested food.
   3. Wall of small intestine is richly supplied with blood vessels which take the absorbed food to different body part.

50. Match the words of column A with column B.

Answer :

Words of column A are matched with that of column B as below:

51. Why is the rate of breathing in aquatic organisms much faster than in terrestrial organisms?

Answer:

Aquatic organisms depend on dissolved oxygen in water while terrestrial organisms absorb oxygen air. Since concentration of dissolved oxygen is much lower as compared to that of oxygen present in air, aquatic organisms breathe faster to meet the demand oxygen.

Aquatic organisms have same surface for absorption of oxygen and exchange while terrestrial organisms are at advantage as they have different organs for breathing and gaseous exchange.

52. Why is blood circulation in human heart called double circulation?

Answer:

Human heart has four completely separated chambers which allows two completely separated circuits of oxygenated and deoxygenated blood; hence the name, double circulation.

The pulmonary circuit includes flow of blood through heart-lung-heart while systemic circuit includes heart-rest of the body-heart. This ensures that left side of heart receive and pumps only oxygenated blood while the right side receives and pumps only deoxygenated blood.

The blood circulated in human heart is called double circulation because the blood passes through the heart twice during one complete cardiac cycle of the body.

53. What is the advantage of having four chambered heart?

Answer:

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood i.e. double circulation.

a.It ensures complete separation of oxygenated and deoxygenated blood.

b. It allows rapid pumping of oxygenated blood under high pressure which is required by active endothermic animals to maintain the constant body temperature.

54. Mention the major events during photosynthesis.

Answer :

The major events during photosynthesis are

a.Light reaction:

Absorption of sunlight energy by main and accessory photosynthetic pigments (chl a, b, c and carotenoids)

Oxidation of water into oxygen and hydrogen driven by light energy and preservation of released energy in form of ATP and NADPH.

b. Dark reaction:

Reduction of CO2 to produce carbohydrates using energy of ATP and NADPH.

55. In each of the following situations what happens to the rate of photosynthesis?

a. Cloudy days

b. No rainfall in the area

c. Good manuring in the area

d. Stomata get blocked due to dust

Answer:

a.Cloudy days will cause the rate of photosynthesis to decrease due to the low availability of sunlight.

b. No rainfall in the area will cause the rate of photosynthesis to decrease due to the low availability of water.

c. Good manuring in the area will cause the rate of photosynthesis to decrease due to the improved availability to minerals necessary for plant growth and development.

d. Stomata get blocked due to dust will cause the rate of photosynthesis to decrease due to the disturbed carbon dioxide intake through stomata.

56. Name the energy currency in the living organisms. When and where is it produced?

Answer:

ATP is the energy currency in the living organisms. Cellular respiration is complete oxidation of food substances into carbon dioxide and water to release the stored energy. The final stage of cellular respiration is the step wise flow of electrons through or within a membrane from a reduced compound to electron acceptor accompanied by ATP synthesis. It occurs in inner mitochondrial membrane.

57. What is common for Cuscuta, ticks and leeches?

Answer:

Cuscuta ticks and leeches, all are parasites. Parasitism is association of two organism wherein one is benefitted at the cost of other partner.

58. Explain the role of mouth in digestion of food.

Answer:

a.The teeth serve the function of mechanical digestion by chewing and grinding.

b.Three pairs of salivary glands in mouth secrete saliva which contain bicarbonate ions and salivary amylase. Salivary amylase starts the chemical digestion of starch into maltose in mouth itself.

c. Tongue serves in mixing of food with saliva.

59. What are the functions of gastric glands present in the wall of the stomach?

Answer :

The gastric glands of stomach produce gastric juice, which contain pepsinogen, HCl and mucus.

HCl impart highly acidic pH to stomach which in turn supports conversion of inactive pepsinogen into active pepsin.

Mucus plays an important role and protects the inner lining of stomach against erosion from hydrochloric acid produced in the stomach.

Pepsinogen is inactive precursor of pepsin and is first converted into active form in acidic environment of stomach to start protein digestion.

60. Match the words of column A with column B.

Answer :

Words of column A are matched with that of column B as below:

Part C : Long Answer Type

61.Explain the process of nutrition in Amoeba.

Answer :

Amoeba follows the holozoic type nutrition. Holozoic refers to engulfment of whole/part of plant or animal in liquid or solid state. The heterotrophic Amoeba engulf the particulate food. The process of obtaining food by Amoeba is called phagocytosis. It is carried out as per the following steps:

1. Ingestion : Engulfment of food particle by forming temporary projections called pseudopodia is called as ingestion. The engulfed food is taken inside the body by pinching off the food vacuole of pseudopodia.

2. Digestion : Breakdown of complex substances into simpler ones by digestive enzymes takes place in food vauole only.

3. Absorption: The digested food present diffuses from food vacuole into the cytoplasm causing disappearance of food vacuole.

4. Assimilation : Food absorbed is used by Amoeba for various metabolic processes.

5. Egestion : The waste products of Amoeba are disposed off in surrounding water by the process of simple diffusion through its cell membrane or body surface.

62. Describe the alimentary canal of man.

Answer :

Human alimentary canal consists of organs of digestion which are namely, in sequence, mouth, oesophagus, stomach, small intestine, large intestine and anus.

Mouth cavity – It is the oral cavity inside mouth, containing teeth, tongue and three pairs of salivary glands.

Pharynx – The oral cavity opens into the pharynx. It is the part where food passage and air passage cross each other.

Esophagus – It is a long muscular, tube that passes through thoracic cavity and diaphragm into abdominal cavity and carries the food down to the stomach by peristalsis.

Stomach – The stomach is a thick-walled, J-shaped organ present on the left side of the abdominal cavity and is continuous with the esophagus above and the duodenum of the small intestine below.

Small intestine – The pyrolic valve of stomach leads to a tubular structure called as small intestine. It has three divisions, i.e., duodenum, jejunum and ileum.

Large intestine – The ileocecal valve of small intestine leads to large intestine, which can be divided into two parts as anterior colon and posterior rectum.

The rectum opens at the anus, which in turn serves as site of defecation, the expulsion of feces.

63. Explain the process of breathing in man.

Answer:

Breathing in humans involves inspiration and expiration that are explained below:

1. Inspiration: Inspiration, the active phase of ventilation includes contraction of diaphragm and the external intercostals muscles and movement of rib cage upward and outward. Deep inspiration involves contraction and lowering down of diaphragm to facilitate expansion of lungs by increasing volume of thoracic cavity. The expansion of thoracic cavity and expansion of lungs create the air pressure difference outside the lung and alveoli to facilitate flow of air into alveoli.
2. Expiration : It is passive phase of breathing that involves relaxed stage of diaphragm and intercostals muscles causing downward and inward movement of rib cage. This causes decreased volume of thoracic cavity and recoiling lungs. The resultant increased air pressure in alveoli as compared to atmospheric pressure causes air to move outside the body.

64. Explain the importance of soil for plant growth.

Answer:

Soil is important for plant growth due to the reasons given below:

1. Anchorage: Soil holds the plants and provides the base on which all the terrestrial and some aquatic plants grow.
2. Source of water and mineral: Soil serves as reservoir of water and minerals absorbed by plant roots to support growth and development.
3. The roots of a plant also take the oxygen required for respiration from the soil particles by the process of diffusion.
4. Symbiotic association of plants with soil microbes help plant absorb otherwise unavailable nutrients such as nitrogen.

65. How do carbohydrates, proteins and fats get digested in human beings?

Answer :

Digestion of carbohydrates :

1. Oral cavity – Salivary amylase present in saliva breaks down starch into maltose.
2. Small intestine – Pancreatic amylase presents in pancreatic juice breakdown the remaining starch into maltose. Maltase of intestinal juice breakdown maltose into glucose units.

Digestion of proteins:

1. Mouth does not have any digesting enzyme for proteins and hence proteins digestion does not start in oral cavity.
2. Stomach pepsin is a protein digesting enzyme secreted by chief cells of stomach wall in its inactive form called as pepsinogen which in turn is converted into active pepsin upon exposure to HCl. Pepsin starts protein digestion into small peptides.
3. Small intestine- Pancreatic juice secretes trypsinogen, chymotripsinogen, trypsin and chymotrypsin digest proteins into peptides. Peptidases of intestinal juice digest the peptides into amino acids.

Digestion of fats:

1. Small intestine:

a.Emulsification of large globules of fats into smaller droplets by bile salt.

b.Pancreatic lipase digests the emulsified fat globules into glycerol and fatty acids.

c.Glycerol and fatty acids enter the villi cells where they are rejoined and packaged and lipoprotein droplets before entering the lacteals.

66. Explain the mechanism of photosynthesis.

Answer:

Photosynthesis is the process involving production of carbohydrates by using carbon dioxide as a chief carbon source and water as electron donor. Photosynthesis can be divided into two phases:

a.Light reactions: Since these reactions cannot take place in absence of light, they are called as light dependent reactions or light reactions. It includes:

• Absorption of sunlight energy by main and accessory photosynthetic pigments.
• Oxidation of water into oxygen and hydrogen driven by light energy and preservation of released energy in form of ATP and NADPH.

b.Dark reaction: Since these reactions do not require sunlight and can occur in presence or absence of sunlight, they are termed as dark reaction or light independent reactions.

• Reduction of CO₂ to produce carbohydrates using energy of ATP and NADPH.
• The extra glucose is stored as starch in the leaves of the plant.

67.Explain the three pathways of breakdown in living organisms.

Answer:

Cellular respiration is the process of breakdown of food substances into simpler ones to release the stored energy. On the basis of presence or absence of oxygen, it can occur through aerobic or anaerobic pathway.

1. Aerobic respiration: Glucose in the presence of oxygen, breaks down to carbon dioxide and water with release of large amount of energy. It occurs in three steps, glycolysis, citric acid cycle and ETC. Glycolysis is breakdown of glucose into pyruvate. It is oxygen independent pathway occurs in cytoplasm. Pyruvate is decarboxylated into acetyl coA in cytoplasm only. Citric acid cycle is the second phase of cellular respiration in which acetyl Co are enzymatically oxidized into carbon dioxide and the released energy is stored in NADH and FADH2. Electron transport chain includes downhill flow of electrons to final electron acceptor through a chain of membrane- bound carriers to facilitate the uphill transport of protons across a proton-impermeable membrane and ATP synthesis. Enzymes of citric acid cycle are present in mitochondrial matrix while the electron transport chain is present in inner mitochondrial membrane, hence, the last two phases of aerobic respiration takes place in mitochondria only.
2. Anaerobic respiration: Glycolysis is breakdown of glucose into pyruvate. It is oxygen independent pathway and is common to both aerobic and anaerobic respiration. Fate of pyruvate depends on oxygen availability. Anaerobic respiration can occur via lactic acid fermentation or alcohol fermentation.

Alcohol fermentation : Due to limited oxygen availability, pyruvate remains in cytoplasm where pyruvate decarboxylase and alcohol dehydrogenase enzymes carry out the second phase of anaerobic respiration and produce ethanol and carbon dioxide with limited amount of energy being released.

Lactic acid fermentation: Due to limited oxygen availability, pyruvate remains in cytoplasm where it is broken down into lactic acid with limited amount of energy being released.

68.Describe the flow of blood through the heart of human beings.

Answer :

Human heart has four completely separated chambers which allow two completely separated circuits of oxygenated and deoxygenated blood; hence the name, double circulation.

The pulmonary circuit includes flow of blood through heart-lung-heart while systemic circuit includes heart-rest of the body-heart. This ensures that left side of heart receives and pumps only oxygenated blood while the right side receives and pump only deoxygenated blood.

Two pulmonary veins come from each lung and pas O2 rich blood to left atrium. The left ventricle pumps blood into the aorta which in turn branches and delivers blood to the major body regions and organs. The anterior vena cava collects deoxygenated blood from the head, chest and arms and enters the right atrium while the inferior vena cava collects blood from the lower body regions. Both venae cavae pass the deoxygenated blood to the right atrium. Blood from right atrium enters right ventricle and pulmonary arteries carry deoxygenated blood from right ventricle to lungs for oxygenation.

69. Describe the process of urine formation in kidneys.

Answer:

Urine formation occurs in the kidneys involves the following steps:

1. Glomerular filtration - Glomerular filtration is passive filtration of the blood that starts with entry of blood through glomerulus, a special ball of capillaries. The overall process leads to removal of 15-25% water and solutes from the plasma entering the glomerulus. Filtration of any substance through glomerular filtration depends on molecular size, protein binding, ionization, polarity and working conditions of kidney in general.
2. Tubular reabsorption - glomerular filtrate enters the proximal convoluted tubule wherein nutrient and salt molecules are actively reabsorbed and pushed into the peritubular capillary network while water flows passively. The filtrate is now composed of urea, some salts and water.
3. Tubular secretion – It includes active secretion of certain substances from the peritubular capillary network into the distal convoluted tubule. The urine formed is collected in the urinary bladder.

Chapter 7 : Control and Coordination

Part A : Multiple Choice Questions

1.Which of the following statements is correct about receptors?

a. Gustatory receptors detect taste while olfactory receptors detect smell.

b. Both gustatory and olfactory receptors detect smell.

c. Auditory receptors detect smell and olfactory receptors detect taste.

d. Olfactory receptors detect taste and gustatory receptors smell.

Answer : a

Explanation:

Gustatory receptors are the taste receptors which are present on the surface of tongue in the form of taste buds. Olfactory receptors help to sense the smell and are located over the roof of nasal cavity.

2.Electrical impulse travels in a neuron from

a.Dendriteà Axon à Axonal end à Cell body

b. Cell body à Dendrite à Axon à Axonal end

c. Dendrite à Cell body à Axon à Axonal end

d. Axonal end à Axon à Cell body à Dendrite

Answer : c

Explanation:

Dendrite receives signals from sensory receptors or other neurons. Axon serves to conduct the nerve impulse away from the cell body.

3.In a synapse, chemical signal is transmitted from

a.Dendritic end of one neuron to axonal end of another neuron.

b. Axon to cell body of the ame neuron to axonal end of another neuron.

c. Cell body to axonal end of the same neuron

d. Axonal end of one neuron to dendritic end of another neuron.

Answer : d

Explanation :

Neurotransmitters are released from axon of one neuron to dendrite of next neuron.

4. In a neuron, conversion of electrical signal to a chemical signal occurs at

a.Cell body

b. Axonal end

c. Dendritic end

d. Axon

Answer: b

Explanation :

Neurotransmitters are released from axonal end of one neuron and transmit the electrical signal to dendrite of next neuron.

5. Which is the correct sequence of the components of a reflex arc?

a. Receptors à Muscles à Sensory neuron à Motor neuron àSpinal cord

b. Receptors à Motor neuron à Spinal cord à Sensory neuron àMuscle

c. Receptors à Spinal cord à Sensory neuron à Motor neuron à Muscle

d. Receptors àSensory neuronàSpinal cordà Motor neuron à Muscle

Answer: d

Explanation:

A stimulus received by the receptors present on skin, is transmitted to the sensory neuron which carries it to the central nervous system (the spinal cord and brain). A motor neuron carries the message from the central nervous system to the effector which could be a muscle, a gland or both.

6.Which of the following statements are true?

(i) Sudden action in response to something in the environment is called reflex action.

(ii) Sensory neurons carry signals from spinal cord to muscles.

(iii)Motor neurons carry signals from receptors to spinal cord.

(iv)The path through which signals are transmitted from a receptor to muscle or a gland is called reflex arc.

a.(i) and (ii)

b. (i) and (iii)

c. (i) and (iv)

d. (i) , (ii) and (iii)

Answer: c

Explanation :

Reflex arc is a simple nervous pathway and consists of sensory receptor, afferent neuron, centre, efferent neuron and effector organ. Automatic, quick and innate response to particular stimuli that is mediated by reflex arc is known as reflex action.

7.Which of the following statements are true about the brain?

(i) The main thinking part of brain in hind brain.

(ii) Centres of hearing, smell, memory, sight, etc., are located in fore brain.

(iii)Involuntary actions like salivation, vomiting, blood pressure are controlled by the medulla in the hind brain.

(iv)Cerebellum does not control posture and balance of the body.

a.(i) and (ii)

b. (i), (ii) and (iii)

c. (ii) and (iii)

d. (iii) and (iv)

Answer : c

Explanation :

Cerebrum is the center for higher thought processes required for learning memory, language and speech. Medulla is the center for regulation of involuntary actions.

8.Posture and balance of the body is controlled by

a.Cerebrum

b.Cerebellum

c.Medulla

d.Pons

Answer: b

Explanation:

Cerebellum coordinates the voluntary movements of skeletal muscles as well as posture, balance and equilibrium.

9. Spinal cord originates from

a.Cerebrum

b.Medulla

c.Pons

d.Cerebellum

Answer: b

Explanation :

Spinal cord begins in continuation with medulla and extends downwards.

10.The movement of shoot towards light is

a.Geotropism

b.Hydrotropism

c.Chemotropism

d.Phototropism

Answer: d

Explanation:

Growth movement of plants in response to light is called as phototropism.

11.The main function of abscisic acid in plants is to

a.Increase the length of cells

b.Promote cell division

c.Inhibit growth

d.Promote growth of stem

Answer: c

Exaplanation:

Abscisic acid is a growth retardation hormone.

12. Which of the following is not associated with growth of plant?

a.Auxin

b.Gibberellins

c.Cytokinins

d.Abscisic acid

Answer : d

Explanation:

Abscisic acid is a growth retardation hormone.

13.Iodine is necessary for the synthesis of which hormone?

a.Adrenaline

b.Thyroxin

c.Auxin

d.Insulin

Answer: b

Explanation :

Hormones of thyroid gland have iodine as their structural component.

14.Choose the incorrect statement about insulin.

a.It is produced from pancreas.

b.It regulates growth and development of the body.

c. It regulates blood sugar level.

d. Insufficient secretion of insulin will cause diabetes.

Answer: b

Explanation:

Insulin regulates blood sugar level.

15. Select the mis-matched pair

a.Adrenaline – Pituitary gland

b. Testosterone – Testes

c. Estrogen – Ovary

d. Thyroxin – Thyroid gland

Answer: a

Explanation :

Adrenaline is secreted by the adrenal gland.

16. The shape of guard cells changes due to change in the

a.Protein composition of cells

b.Temperature of cells

c.Amount of water in cells

d.Position of nucleus in the cells

Answer: c

Explanation :

Shape of guard cell is maintained by its turgidity which in turn is regulated by water content of these cells.

17.The growth of tendril in pea plants is due to

a.Effect of light

b.Effect of gravity

c.Rapid cell divisions in tendrillar cells that are away from the support

d.Rapid cell divisions in tendrillar cells in contact with the support.

Answer : c

Explanation :

Growth movements in response to touch are known as thigmotropism.

18. The growth of pollen tubes towards ovules is due to

a.Hydrotropism

b.Chemotropism

c.Geotropism

d.Phototropism

Answer: b

Explanation :

Stigma serves as landing platform for pollen as well as secretes chemical substances that attract pollen tube through style towards ovary.

19.The movement of sunflower in accordance with the path of sun is due to

a.Phototropism

b.Geotropism

c.Chemotropism

d.Hydrotropism

Answer: a

Explanation :

Growth movement of plants in response to light is called as phototropism.

20. The substance that triggers the fall of mature leaves and fruits from plants is due to

a.Auxin

b.Gibberellins

c.Abscisic acid

d.Cytokinin

Answer : c

Explanation:

Abscisic acid serves to form of layer of abscission.

21. Which of the following statements about transmission of nerve impulse is incorrect?

a. Nerve impulse travels from dendritic end towards axonal end

b.At the dendritic end electrical impulses bring about the release of some chemicals which generate an electrical impulse at the axonal end of another neuron.

c.The chemicals released from the axonal end of one neuron cross the synapse and general a similar electrical impulse in a dendrite of another neuron.

d.A neuron transmits electrical impulses not only to another neuron but also to muscle and gland cells.

Answer : b

Explanation:

Neurotransmitters are released from axon of one neuron to dendrite of next neuron.

22.Involuntary actions in the body are controlled by

a.Medulla in fore brain

b.Medulla in mid brain

c.Medulla in hind brain

d.Medulla in spinal cord

Answer : c

Explanation :

Medulla is part of hind brain and ocntrols the involuntary action.

23.Which of the following is not an involuntary action?

a.Vomiting

b.Salivation

c.Heart beat

d.Chewing

Answer: d

Explanation:

The actions that are not under our direct control are called as involuntary actions.

24.When a person is suffering from severe cold, he or she cannot

a.Differentiate the taste of an apple from that of an ice cream.

b.Differentiate the smell of a perfume from that of an agarbatti.

c.Differentiate red light from green light.

d.Differentiate a hot object from a cold object.

Answer : b

Explanation:

Cold thickens the mucus in nasal passages and block passage of odour to olfactory receptor cells.

25.Which statement is not true about thyroxin?

a.Iron is essential for the synthesis of thyroxin.

b.It regulates carbohydrates, protein and fat metabolism in the body.

c.Thyroid gland requires iodine to synthesise thyroxin.

d.Thyroxin is also called thyroid hormone.

Answer : a

Explanation :

Thyroxin contains iodine in its structure.

27.Dwarfism results due to

a.Excess secretion of thyroxin

b.Less secretion of growth hormone

c.Less secretion of adrenaline

d. Excess secretion of growth hormone

Answer : b

Explanation :

Growth hormone regulates normal growth and development of individual.

28.Dramatic changes of body features associated with puberty are mainly because of secretion of

a.Estrogen from testes and testosterone from ovary.

b.Estrogen from adrenal gland and testosterone from pituitary gland.

c.Testosterone from testes and estrogen from ovary.

d.Testosterone from thyroid gland and estrogen from pituitary gland.

Answer : c

Explanation :

Testosterone and estrogen are male and female sex hormones respectively.

29. A doctor advised a person to take an injection of insulin because

a.His blood pressure was low

b. His heart was beating slowly

c.He was suffering from goitre

d.His sugar level in blood was high.

Answer: d

Explanation: Insulin regulates the blood sugar level.

30.The hormone which increase the fertility in males is called

a.Oestrogen

b.Testosterone

c.Insulin

d.Growth hormone

Answer: b

Explanation :

Testosterone is the male sex hormone necessary for sperm production.

31.Which of the following endocrine glands is unpaired?

a. Adrenal

b.Testes

c. Pituitary

d.Ovary

Answer: c

Explanation : Pituitary gland is unpaired gland.

32. Junction between two neurons is called

a.Cell junction

b.Neuro muscular junction

c.Neural joint

d.Synapse

Answer : d

33. In humans, the life processes are controlled and regulated by

a.Reproductive and endocrine systems

b.Respiratory and nervous systems

c.Endocrine and digestive systems

d.Nervous and endocrine systems

Answer: d

Explanation: Nervous system and endocrine system work together to maintain homeostasis.

Part B : Short Answer Type

34. Name the plant hormones responsible for the following:

a.Elongation of cells

b.Growth of stem

c.Promotion of cell division

d.Falling of senescent leaves

Answer:

a.Elongation of cells : Auxin

b.Growth of stem : Gibberellin

c.Promotion of cell division : Cytokinin

d.Falling of senescent leaves : Abscisic acid

35. Label the endocrine gland in figure:

Answer :

a.Pineal gland

b.Pituitary gland

c.Thyroid gland

d.Thymus gland

36. Label the parts a, b, c and d and show the direction of flow of electrical signals in given figure.

Answer :

a.Sensory neuron

b.Spinal cord

c.Motor neuron

d.Effector

Direction of flow of electric signal is as shown below:

Sensory receptor à Sensory neuron à Spinal cord à Motor neuron à Effector organ

37. In figure a, b and c, which appears more accurate and why?

Answer :

Figure (a) is more accurate. Roots of plants are positive geotropic and grown downwards while stem is positive phototropic and grows upwards.

38. Label the part of a neuron in figure given below.

Answer :

a.Dendrite

b.Cell body

c.Axon

d.Nerve ending

39. Match the terms of column A with those of column B.

Answer :

The matching of the column A with column B is :

40. What is a trophic movement? Explain with an example.

Answer:

The directional growth movements of plants due to an external stimuli are called tropic movements. It can be either towards the stimulus, or away from it.

Growth of plant in response to light is known as phototropism. For example, shoots and stem of the plant grow upwards hence show positive phototropism.

Growth of plant in direction of gravity is known as geotropism. For example, roots of plants are grow downwards hence show positive geotropism.

41. What will happen if intake of iodine in our diet is low?

Answer:

Thyroid gland produces thyroxine and triodothyronine. Thyroxine has four iodine atoms while triiodothyronine has three iodine atoms. The dietary iodine serves as source and thus iodine deficient diet renders the gland unable to synthesize the hormones. Thyroid hormones deficiency inhibits metabolic rate, growth and development.

A person might suffer from goitre in case of iodine deficiency in the body.

42. What happens at the synapse between two neurons?

Answer:

Synapse is the junction between two neurons. Electrical impulse at the axonal end stimulates the axon bulb to release chemical which in turn diffuses across the synapse. The chemical serves to stimulate the dendrites of adjacent neuron which in turn send electrical signals to their cell body to be carried along the axon.

43.Answer the following :

a.Which hormone is responsible for the changes noticed in females at puberty?

b.Dwarfism results due to deficiency of which hormone?

c.Blood sugar level rises due to deficiency of which hormone?

d.Iodine is necessary for the synthesis of which hormone?

Answer:

a.Oestrogen is responsible for development of secondary sexual characters in females at puberty.

b. Growth hormone promotes growth and development of the body.

c.Insulin controls blood sugar level by stimulating oxidation of glucose and absorption of glucose by liver and muscle cells.

d.Iodine is necessary for the synthesis of thyroxine. It is a thyroid hormone that regulates the metabolism in the body.

44.Answer the following:

a.Name the endoocrine gland associated with brain?

b.Which gland secretes digestive enzymes as well as hormones?

c.Name the endocrine gland associated with kidneys.

d.Which endocrine gland is present in males but not in females?

Answer:

a.Pituitary gland located in the groove of sphenoid bone of the skull in the brain.

b.Pancreas secretes the pancreatic juice and hormones insulin and glucagon.

c.Adrenal glands are located on the top of two kidneys.

d.Testes are present only in males which secrete male sex hormone, testosterone.

Part C : Long Answer Type

45.Draw the structure of a neuron and explain its functions.

Answer:

Neuron is the structural and functional units of nervous system. It serves to carry nerves impulse from one part of body to other. It has dendrites, cell body and axon. Dendrite receives signals from sensory receptors or other neurons. The long extension of cell body of nerve cell is called as axon that serves to conduct the nerve impulse away from the cell body. Cell body is the metabolic center of neuron.

46.What are the major parts of the brain? Mention the function of different parts.

Answer :

Brain is the most important coordinating center in the body. It has three major parts namely: fore-brain, mid-brain and hind brain.

1. Fore brain:

2. Mid brain:

3. Hind brain

47.What constitutes the central and peripheral nervous systems? How are the components of central nervous system protected?

Answer :

The central nervous system consists of the brain and the spinal cord.

1. Brain is the main centre of coordination of sensory information in the body. It is located in protective brain box or cranium and is covered by membranous meninges. Cerebrospoinal fluid is the clear tissue fluid which makes protective cushion around and within CNS. It is present in central canal of spinal cord and in brain ventricles.
2. Spinal cord is a long cylindrical structure that begins from the medulla oblongata and extends downwards. It is enclosed in a protective bony cage vertebral column and is also surrounded by meninges.

Peripheral Nervous System : It lies outside the central nervous system and consists of somatic and autonomic nervous system.

It includes cranial, spinal and visceral nerves.

(i)Cranial nerves: These consist of the 12 pairs that emerge from the brain mostly concerned with head, neck and facial region of the body.

(ii)Spinal nerves : 31 pairs of spinal nerves arise from the spinal cord and spread throughout the body.

(iii)Visceral nervous : These arise from he spinal cord and are connected to the internal organs of the body.

48.Mention one function for each of these hormones.

a.Thyroxin

b.Insulin

c.Adrenaline

d.Growth hormone

e.Testosterone

Answer :

49.Name various plant hormones. Also give their physiological effects on plant growth and development. Also give their physiological effects on plant growth and development.

Answer :

50.What are the reflex actions? Give two examples. Explain a reflex arc.

Answer :

Reflex action:

A reflex action, is an involuntary and nearly instantaneous movement in response to a stimulus.

For example:

1. Moving away your hand upon touching a hot object.
2. Closing your eyes on sudden exposure to bright light.

Reflex arc:

Reflex arc is a simple nervous pathway and consists of receptors, sensory neurons, interneurons, motor neurons and muscles. The sensory neurons transmit the sensory information from sensory receptors to spinal cord or brain. The interneurons integrate the incoming information and signal is relayed to motor neurons. The motor pathway transmits the signal from motor neurons to the effector organs.

51.’Nervous and hormonal systems together perform the function of control and coordination in human beings. Justify the statement.

Answer :

Nervous system serves to pass the sensory information from receptor to effector organs and thereby generate response. The afferent or sensory neurons transmit the sensory information from sensory receptors to spinal cord or brain. The interneurons integrate the incoming information and signal is relayed to motor or efferent neurons. The efferent or motor pathway transmits the signal from motor neurons to the effector organs.

The effector organs generate response in terms of secretion of either any activity or secretion of hormones. It can be said that secretion of hormones is under regulation of nervous system. Hormonal system can regulate wise range of target tissues as compared to nervous system. Hence, together, nervous system and hormonal system serve the function of control and coordination.

52.How does chemical coordination take place in animals?

Answer :

Hormones are the long-range chemical messengers that are released into blood by endocrine gland in response to some signal. These hormones exert their effect on the target cells present distantly from their site of release. These hormones sere the function of chemical coordination in animals.

Hormones are released into the blood stream and can reach all cells but they affect or target cells. This is followed by generation of stimulus specific biochemical or physiological activity. In this way, hormones regulate functioning of different organs and tissues. Each hormone is under regulation of feedback mechanism which in turn ensures reliability of the system.

53.Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?

Answer :

Two neurons are never in physical contact of each other and the junction between two neurons is referred to as synapsis. The synapse serves like a one-way valve as axonal ends of synapse release the chemical substance that diffuse into synapse. This chemical diffuses towards the dendrite end of next neuron and propagates an electric signal.

Diffusion of chemical from axonal end followed by its diffusion in synapse and fusion with dendrite of next neuron ensures the transmission of electrical signal. Since, the dendritic end of neuron does not release the chemicals; the nerve impulse can go across only in ono direction.

Chapter 8 : How Do Organisms Reproduce

Part A : Multiple Choice Questions

1.In the list of organisms given below, those that reproduce by the asexual method are

(i)Banana

(ii)Dog

(iii)Yeast

(iv)Amoeba

a.(ii) and (iv)

b.(i),(iii) and (iv)

c.(i) and (iv)

d.(ii),(iii) and (iv)

Answer: b

Explanation:

Among the given options, Amoeba (binary fission), yeast (budding) and banana (vegetative propagule) reproduce by asexual reproduction whereas dogs reproduce by sexual method.

2.In a flower, the parts that produce male and female gametes (germ cells) are

a.Stamen and anther

b.Filament and stigma

c.Anther and ovary

d.Stamen and style

Answer: c

Explanation:

Another produce pollen through microsporogenesis and ovary produce egg cell by megasporogenesis.

3.Which of the following is the correct sequence of events of sexual reproduction in a flower?

a.Pollination, fertilisation, seedling, embryo

b. Seedling, embryo, fertilisation, pollination

c.Pollination, fertilisation, embryo, seedling

d. Embryo, seedling, pollination, fertilization

Answer: c

Explanation:

In pollination, pollen grains transfer from stamen to stigma after which fertilization takes place during which germ cells fuse together to form zygote which in turn leads to embryo formation. Fertilized ovule becomes seed and seeds germinate to produce seedling.

4.Offspring formed by asexual method of reproduction have greater similarity among themselves because

(i)Asexual reproduction involves only one parent

(ii)Asexual reproduction does not involve gametes

(iii)Asexual reproduction occurs before sexual reproduction

(iv)Asexual reproduction occurs after sexual reproduction

a.(i) and (ii)

b.(i) and (iii)

c.(ii) and (iv)

d.(iii) and (iv)

Answer: a

Explanation:

Asexual reproduction does not involve gamete formation and fertilization.

5.Characters transmitted from parents to offspring are present in

a.Cytoplasm

b.Ribosome

c.Golgi bodies

d.Genes

Answer: d

Explanation:

Genes are the stretch of DNA and determine genetic characters.

6.Characters that are transmitted from parents to offspring during reproduction s