Class 10 Science Chapter 1 Assertion and Reason Questions - Chemical Reactions and Equations

Question 1: 

Assertion (A): Carbon dioxide turns lime water milky. Reason 

(R): Carbon dioxide sullies the water. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (c)

Explanation: Carbon dioxide reacts with lime water (calcium hydroxide) to form a milky precipitate of calcium carbonate. The reason given is incorrect as it does not explain the chemical reaction involved.

Question 2: 

Assertion (A): After whitewashing the walls, a shiny white finish on walls is obtained after two to three days. 

Reason (R): Calcium oxide reacts with carbon dioxide to form calcium hydrogen carbonate which gives a shiny white finish. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (c)

Explanation: After whitewashing, the shiny finish is due to the formation of calcium carbonate, not calcium hydrogen carbonate. Calcium hydroxide in the whitewash reacts with carbon dioxide to form calcium carbonate over a few days.

Question 3: 

Assertion (A): A chemical reaction becomes faster at higher temperatures. 

Reason (R): At higher temperatures, molecular motion becomes more rapid. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (a)

Explanation: Higher temperatures increase the kinetic energy of molecules, leading to more frequent and energetic collisions, thus speeding up chemical reactions.

Question 4: 

Assertion (A): To dilute sulfuric acid, acid is added to water and not water to acid. 

Reason (R): Specific heat of water is quite large. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (a)

Explanation: Adding water to acid can cause an exothermic reaction that may splash the acid. Adding acid to water ensures the heat is absorbed safely by the larger volume of water, preventing splashing.

Question 5: 

Assertion (A): Sodium metal is stored under kerosene. 

Reason (R): Metallic sodium melts when exposed to air. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (c)

Explanation: Sodium is highly reactive and stored under kerosene to prevent it from reacting with moisture and oxygen in the air. The reason given is incorrect because sodium does not melt but reacts vigorously when exposed to air.

Question 6: 

Assertion (A): Corrosion of iron is commonly known as rusting. 

Reason (R): Corrosion of iron occurs in the presence of water and air. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (b)

Explanation: Rusting is the specific term for the corrosion of iron, which requires the presence of both water and air. While both statements are true, the reason is not the explanation of the assertion but rather a condition for it.

Question 7: 

Assertion (A): A reducing agent is a substance which can either accept electrons. 

Reason (R): A substance which helps in oxidation is known as a reducing agent. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (d)

Explanation: A reducing agent donates electrons and gets oxidized itself. Therefore, the assertion is incorrect, but the reason correctly defines a reducing agent.

Question 8: 

Assertion (A): Calcium carbonate when heated gives calcium oxide and water. 

Reason (R): On heating calcium carbonate, a decomposition reaction takes place. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (d)

Explanation: When calcium carbonate (CaCO₃) is heated, it decomposes to form calcium oxide (CaO) and carbon dioxide (CO₂), not water. Hence, the assertion is incorrect, while the reason is correct.

Question 9: 

Assertion (A): White silver chloride turns grey in sunlight. 

Reason (R): Decomposition of silver chloride in presence of sunlight takes place to form silver metal and chlorine gas. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (a)

Explanation: The decomposition of silver chloride in the presence of sunlight is a photochemical reaction where it decomposes into silver metal and chlorine gas, causing the color change.

Question 10: 

Assertion (A): In a reaction of copper with oxygen, copper serves as a reducing agent. 

Reason (R): The substance which gains oxygen in a chemical reaction is a reducing agent. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (d)

Explanation: A reducing agent loses electrons and gets oxidized. Copper acts as a reducing agent because it donates electrons, but the reason incorrectly states that a reducing agent gains oxygen, which is actually the process of oxidation.

Question 11: 

Assertion (A): Fe₂O₃ + 2Al → Al₂O₃ + 2Fe is an example of a displacement reaction. 

Reason (R): Aluminium being more reactive than iron displaces Fe from its oxide. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (a)

Explanation: This is a displacement reaction where aluminum, being more reactive, displaces iron from iron oxide to form aluminum oxide and free iron.

Question 12: 

Assertion (A): Quicklime reacts vigorously with water releasing a large amount of heat. 

Reason (R): The above chemical reaction is an exothermic reaction. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (a)

Explanation: When quicklime (calcium oxide) reacts with water, it forms calcium hydroxide and releases a large amount of heat, making the reaction exothermic.

Question 13: 

Assertion (A): Photosynthesis is considered an endothermic reaction. 

Reason (R): Energy gets released in the process of photosynthesis. 

(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.

Correct Answer: (c)

Explanation: Photosynthesis is an endothermic reaction because it absorbs energy from sunlight. The reason incorrectly states that energy is released during photosynthesis.