Answer: Option (A) is the correct answer.
Explanation:
Density is defined as the degree of compactness or mass per unit volume of a substance.
When air expands then it means its molecules have gained kinetic energy. Therefore, they are colliding with each other and result in expansion of air.
So, expansion makes air less dense as mass per unit volume decreases on expansion. Therefore, air rises on expansion.
Thus, we can conclude that air expands, becomes less dense, and rises describes the relationship correctly.
