Assertion (A): One mole of a gas occupies 24.4 litres at S.T.P.

Reason (R): The mass of one mole of a gas is equal to its molecular mass.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

A is false but R is true.

Explanation — At S.T.P. (Standard Temperature and Pressure), one mole of a gas actually occupies 22.4 litres, not 24.4 litres, so Assertion (A) is false.

Reason (R) is true because by definition, the mass of one mole of a substance equals its molecular mass in grams.