Chemical Reactions and Equations

NCERT Exemplar Problems

MCQs Part 2

Question 11: 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. (i) only
2. (ii) only
3. (iv) only
4. (ii) and (iv)

Answer: (d) (ii) and (iv)

Explanation

Barium and Ammonia are displacing each other from their respective salts. So, statement (iv) is true. Barium sulphate appears as precipitate at the end of this reaction. So, statement (ii) is true.

Question 12: 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) 2:1

Explanation

Water molecule is composed of two atoms of hydrogen and one atom of oxygen.

Question 13: 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. (i) and (iii)
2. (ii) only
3. (iii) only
4. (ii) and (iv)

Answer: (d) (ii) and (iv)

Explanation

Heat needs to be supplied for these processes.

Question 14: 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) Lead acetate

Explanation

We need to make lead iodide, so we need a lead compound as reactant. This condition rules out options (c) and (d). Compounds taking place in double displacement reaction should be soluble in water and should break into their ions in aqueous solution.

Question 15: 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) Helium or nitrogen

Explanation

Carbon dioxide and oxygen are reactive gases. So, options (a), (b) and (c) can be easily ruled out. Helium is an inert gas, while nitrogen is almost inert in nature.

Question 16: The following reaction is used for the preparation of oxygen gas in the laboratory

2KClO₃ (s) + heat + catalyst ⇨ 2KCl + 3O₂

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

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) It is a decomposition reaction and endothermic in nature

Explanation

Potassium chlorate decomposes to give potassium chloride and oxygen. Heat is supplied in this reaction. So, option (a) is correct.

Question 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 (l) + O₂ (l) ⇨ 2H₂O (g)
2. 2H₂ (g) + O₂ (l) ⇨ 2H₂O (g)
3. 2H₂ (g) + O₂ (g) ⇨ 2H₂O (l)
4. 2H₂ (g) + O₂ (g) ⇨ 2H₂O (g)

Answer: (c) 2H₂ (g) + O₂ (g) ⇨ 2H₂O (l)

Explanation

Hydrogen and oxygen are available as gases on room temperature, while water is a liquid at room temperature.

Question 18: Which of the following are combination reactions?

1. 2KClO₃ ⇨ 2KCl + 3O₂
2. MgO + H₂O ⇨ Mg(OH)₂
3. 4Al + 3O₂ ⇨ 2Al₂O₃
4. Zn + FeSO₄ ⇨ ZnSO₄ + Fe

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

Answer: (d) (ii) and (iii)

Explanation

A single substance is formed at the end of each of these reactions.