Chemical Reactions and Equations

Exemplar Problems

MCQs part 1

Question 1: Which of the following is not a physical change?

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

Answer: (d) Combustion of Liquefied Petroleum Gas (LPG)

Explanation: A new substance is formed after combustion of any substance. Hence, combustion is a chemical change.

Question 2: The following reaction is an example of a

4NH3 (g) + 5O2 (g) ⇨ 4NO + 6H2O

  1. Displacement reaction
  2. Combination reaction
  3. Redox reaction
  4. Neutralisation reaction
  1. (i) and (iv)
  2. (ii) and (iii)
  3. (i) and (iii)
  4. (iii) and (iv)

Answer: (c) (i) and (iii)

Explanation: Oxygen is displacing hydrogen from NH3. Hence, it is a displacement reaction. Hydrogen is added to oxygen, so it is redox reaction.


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

3Fe (s) + 4H2O (g) ⇨ Fe3O4 (s) + 4H2 (g)

  1. Iron metal is getting oxidised
  2. Water is getting reduced
  3. Water is acting as reducing agent
  4. Water is acting as oxidising agent
  1. (i), (ii) and (iii)
  2. (iii) and (iv)
  3. (i), (ii) and (iv)
  4. (ii) and (iv)

Answer: (c) (i), (ii) and (iv)

Explanation: Oxygen is added to iron, so iron is getting oxidized. Oxygen is removed from water, so water is getting reduced. Water is supplying oxygen for oxidization of iron, so water is acting as oxidizing agent.

Question 4: Which of the following are exothermic processes?

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

Answer: (a) (i) and (ii)

Explanation: Heat is evolved during reaction of water with quick lime. Similarly, heat is evolved during dilution of acid. Processes in options (iii) and (iv) need heat to be supplied. So, these are endothermic processes.


Question 5: Three beakers labelled as A, B and C each containing 25 mL 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. 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. (i) only
  2. (ii) only
  3. (i) and (iv)
  4. (ii) and (iii)

Answer: (c) (i) and (iv)

Explanation: Increase in temperature of solutions contained in beakers A and B shows that these are exothermic processes. Fall of temperature in beaker C shows it is an endothermic process.

Question 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 oxidising agent, it oxidises FeSO4
  2. FeSO4 acts as an oxidising agent and oxidises KMnO4
  3. The colour disappears due to dilution; no reaction is involved
  4. KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound.

Answer: (a) KMnO4 is an oxidising agent, it oxidises FeSO4.

Explanation: KMnO4 is a strong oxidising agent. In acidic medium, it oxidises ferrous sulphate to ferric sulphate.

2KMnO4 + 8H2SO4 + 10FeSO4 → K2SO4 + 5Fe2(SO4)3 + 2MnSO4 + 8H2O

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

  1. Pb + CuCl2 ⇨ PbCl2 + Cu
  2. Na2SO4 + NaCl2 ⇨ BaSO4 + 2NaCl
  3. C + O2 ⇨ CO2
  4. CH4 + 2O2 ⇨ CO2 + 2H2O
  1. (i) and (iv)
  2. (ii) only
  3. (i) and (iii)
  4. (iii) and (iv)

Answer: (b) (ii) Only

Explanation: Reaction in option (i) is an example of single displacement reaction. So, we can easily rule out options (a) and (c). In case of option (ii), sodium and barium are displacing each other from their respective salts. So, this is the correct option.


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

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

Answer: (a) (i) only

Explanation: When halide of silver is exposed to sunlight, it decomposes to give silver and halogen. In this reaction, there is decomposition of silver halide. So, statement (i) is true. Chlorine gas is evolved and silver chloride is undergoing decomposition, so statement (iii) is false.

Question 9: 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 presence of air at high temperature

Answer: (d) Heating copper wire in presence of air at high temperature

Explanation: No new substance is formed in rest of the options.

Question 10: 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 slaking of lime and the solution formed?

  1. It is an endothermic reaction
  2. It is an 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) (ii) and (iii)

Explanation: Liberation of heat indicates that it is an exothermic reaction. So, statement (i) is true. We know that oxides of metals are alkaline in nature. So, aqueous solution of metallic oxide will have pH more than seven. Hence, statement (iii) is true.



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