Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: Hot air balloon rises up in sky, because hot air is less dense than cold air.
Reason R: Volume of a gas decreases on heating.

In the light of the above statements, choose the most appropriate answer from the options given below.

A is correct but R is not correct

The correct answer is Option (3) → A is correct but R is not correct

Assertion A: Hot air balloon rises up in sky, because hot air is less dense than cold air:

Correct: Hot air balloon has hot air inside. Also hot air is less dense than cooler air which surrounds the hot air balloon. This means hot air is lighter than equal volume of cold air. Hence due to buoyant force of cold air, the balloon rises.

Reason R: Volume of a gas decreases on heating:

Incorrect: the volume of a gas actually increases when heated. This is because the average velocity of gas particles increases with temperature, which increases the distance they travel and therefore the volume of the gas. This is known as Charles's Law. 

Hence,  option (3) is the correct answer.