NCERT Class 10 Exemplar - Science

Grade X - Chemistry

Reviewed By:
Krishna Kant Majee
M.Sc., B.Ed.

Chapter 1-Chemical Reactions and Equations-MCQs

Q.1. Which of the following is not a physical change?
(a) Boiling of water to give water vapour
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)

Answer. (d)

Explanation: A physical change involves only change in physical state whereas a chemical change results the formation of new substances. Boiling of water, melting of ice and dissolution of salt are physical changes as no new products are formed.

Q.2. The following reaction is an example of a
$4NH_{3} (g) + 5O_{2}(g) \rightarrow 4NO (g) + 6 H_{2}O (g)$
1. Displacement reaction
2. Combination reaction
3. Redox reaction
4. Neutralisation reaction
(a) 1 and 4
(b) 2 and 3
(c) 1 and 3
(d) 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 $NH_{3}$ are displaced by oxygen.

Q.3. Which of the following statements about the given reaction are correct?
$3Fe(s) + 4H_{2}O(g)\rightarrow Fe_{3}O_{4}(s) + 4H_{2} (g)$
1. Iron metal is getting oxidized.
2. Water is getting reduced.
3. Water is acting as reducing agent.
4. Water is acting as oxidizing agent.
(a) 1, 2 and 3
(b) 3 and 4
(c) 1, 2 and 4
(d) 2 and 4

Answer. (c)
Explanation: Addition of oxygen to Fe is an oxidation process whereas lose of oxygen from $H_{2}O to H_{2}$ is a reduction step. Since water is source of oxygen therefore it acts as oxidizing agent.

Q.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)
(a) 1 and 2
(b) 2 and 3
(c) 1 and 4
(d) 3 and 4

Answer. (a)
Explanation: Energy is released in exothermic reactions in the form of heat.

Q.5. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous $CuSO_{4}$ 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.
(a) Only 1
(b) Only 2
(c) 1 and 4
(d) 2 and 3

Answer. (c)
Explanation: For an exothermic reaction, heat releases during reaction so temperature increases whereas endothermic reactions proceed with absorption of heat which decrease the temperature of reaction.

Q.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?
(a) KMnO4 is an oxidizing agent, it oxidizes $FeSO_{4}$
(b) $FeSO_{4}$ acts as an oxidizing agent and oxidizes $KMnO_{4}$
(c) The colour disappears due to dilution, no reaction is involved
(d) $KMnO_{4}$ is an unstable compound and decomposes in the presence of $FeSO_{4}$ 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 $FeSO_{4}$ to $Fe_{2}(SO_{4})_{3}$

Q.7. Which among the following is (are) double displacement reaction(s)?
(i)$Pb + CuCl_{2}\rightarrow PbCl_{2} + Cu$
(ii)$Na_{2}SO_{4}\rightarrow BaSO_{4} + 2NaCl$
(iii) $C + O_{2}\rightarrow CO_{2}$
(iv) $CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O$

(a) (i) and (iv)
(b) Only (ii)
(c) (i) and (ii)
(d) (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.

Q.8. Which among the following statement(s) is /are true? Exposure of silver chloride to sunlight for a long duration turns grey due to-
(i) The formation of silver by decomposition of silver chloride.
(ii) Sublimation of silver chloride.
(iii) Decomposition of chlorine gas from silver chloride.
(iv) Oxidation of silver chloride.
(a) (i) Only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) Only (iv)

Answer. (a)
Explanation: In the presence of sunlight, AgCl decompose to form grayish white silver metal and releases chlorine gas.

Q.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 slaking of lime and the solution formed?
(i) It is an endothermic reaction.
(ii) It is exothermic reaction.
(iii) The pH of the resulting solution will be more than seven.
(iv) The pH of the resulting solution will be less than seven.
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (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.

Q.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?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) Only (i)
(b) Only (ii)
(c) Only (iv)
(d) (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.

Q.11. Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is
(a) 1 : 1
(b) 2 : 1
(c) 4 : 1
(d) 1 : 2

Answer. (b)
Explanation: The balance chemical equation for electrolysis of water is;

$\ce{2H_{2}O ->[{Electric Current}] 2H_{2}(g)+ O_{2}(g)}$

Q.12. Which of the following is (are) an endothermic process(es)?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) Both (i) and (iii)
(b) Only (ii)
(c) Only (iii)
(d) Both (ii) and (iv)

Answer. (d)
Explanation: An endothermic process involves absorption of heat such as sublimation and evaporation needs heat energy.

Q.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?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) 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.

Q.14. Which of the following gases can be used for storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) 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.

Q.15. The following reaction is used for the preparation of oxygen gas in the laboratory
$\ce{2KClO_{3} ->[{Heat}][{Catalyst}] 2KCl(s) + 3O_{2}(g)}$
Which of the following statement(s) is/are correct about the reaction?
(a) It is a decomposition reaction and endothermic in nature
(b) It is a combination reaction
(c) It is a decomposition reaction and accompanied by release of heat
(c) 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.

Q.16. Which one of the following processes involve chemical reactions?
(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a China dish in the open
(d) Heating copper wire in the presence of air at high temperature

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

Q.17. In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
(a) $2H_{2} (l) + O_{2} (l)\rightarrow 2H_{2}O (g)$
(b) $2H_{2} (g) + O_{2}(l) \rightarrow 2H_{2}O (g)$
(c) $2H_{2} (g) + O_{2} (g) \rightarrow 2H_{2}O (l)$
(d) $2H_{2} (g) + O_{2} (g)\rightarrow 2H_{2}O (g)$

Answer. (c)
Explanation: At standard conditions, hydrogen and oxygen exist in gaseous state whereas water in liquid state.|

Q.18. Which of the following are combination reactions?
(i) $\ce{2KClO_{3} ->Heat] 2KCl + 3O_{2}}$
(ii) $MgO + H_{2}O\rightarrow Mg(OH)_{2}$
(iii) $ Al + 3O_{2} \rightarrow 2Al_{2}O_{3}$
(iv) $ Zn + FeSO_{4}\rightarrow ZnSO_{4} + Fe $

(a) Both (i) and (iii)
(b) Both (iii) and (iv)
(c) Both (ii) and (iv)
(d) Both (ii) and (iii)

Answer. (d)
Explanation: Combination reactions form a new product with the combination of more than one reactant molecules.