NDA General Ability Question (2025) — Solution

Step-by-step solution

A physical change is a change in which no new substance is formed and the chemical composition of the substance remains exactly the same. The interconversion of states of matter (such as melting of ice or boiling of water) does not alter the chemical composition of the substance, hence it is a physical change. During the burning of a candle, the melting of wax is a physical change, while the combustion of wax to form carbon dioxide and water vapor is a chemical change. Thus, both physical and chemical changes take place. Rusting of iron involves the reaction of iron with oxygen and moisture to form a new chemical compound, hydrated iron(III) oxide. Therefore, it is a chemical change. Since the chemical composition of molecules does not change during a physical change, the statement in option (3) is incorrect. Answer: During a physical change, the chemical composition of molecules changes