Question

Assertion: Burning of coal is a physical change.
Reason: When coal is burnt, the chief component, carbon is changed to carbon dioxide. This process cannot be reversed.
(A) Both assertion and reason are correct and the reason is the correct explanation for the assertion.
(B) Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
(C) Assertion is correct but the reason is incorrect.
(D) Assertion is incorrect but the reason is correct.

Answer 1

Hint: Physical change causes a change in the state of substance but does not change chemical composition. They are usually reversible. In a physical change, there is a change in physical state. In a chemical change, there is a change in chemical composition and they cannot be reversed easily.

Complete step by step solution:
-When coal is burnt, the chief component carbon reacts with the oxygen present in the air and produces carbon dioxide. This is called combustion. Combustion is a chemical reaction. There is a change in chemical composition and this reaction cannot be reversed as carbon dioxide cannot be converted into coal again. Hence, the burning of coal is a chemical change.
-Melting of ice, conversion of water to steam are physical changes. As water can be converted into ice by freezing and steam can be converted into water by condensation. These are examples of physical change as there is a change in the physical state and they are reversible.

Hence, the (D) assertion is incorrect and the reason statement is correct.

Note: when carbon reacts with oxygen in the air, there is a combustion reaction. Combustion reactions are generally irreversible. Burning of coal is chemical change as a chemical reaction is occurring. Boiling, freezing, melting are examples of physical changes.