The volume occupied by the molecules of an ideal gas is:

Hint: According to the postulate of kinetic molecular theory of gases, gas molecules are so small in size. They are so far apart from each other and in random motion. The volume of the gas molecules is negligible in comparison to the total volume of the gas.

Complete step by step answer:
There is an important assumption or postulate, given by kinetic theory of gases, which tells us about the volume occupied by the molecules of an ideal gas. The assumption is:
- The volume occupied by the molecules of an ideal gas is negligible in comparison to the total volume of the gas. This assumption can be explained as:
Gases tend to fill completely any available space or space of a container. Size of the gas molecules is so small and they are tiny spherical in shape. Size of the container in which a gas is filled is so large in comparison to the size of gas molecules. Therefore, it is assumed that volume occupied by molecules of an ideal gas is negligible in comparison to the total volume of the gas and in fact, it is assumed to be zero.
Thus, the required answer is zero, that is, the volume occupied by the molecules of an ideal gas is zero.

Additional Information:
The volume occupied by one mole of an ideal gas at standard temperature (i.e., 273.15K) and pressure (i.e., 1 bar) is 22.711 $dm^3$. The volume occupied by one mole of an ideal gas is known as molar volume of the gas.

Note: The assumption that the volume occupied by the molecules of an ideal gas is zero is one of the causes of deviation from ideal behaviour of gases. The molecules of the gas, however, do occupy a certain volume because gases can be liquefied and solidified at room temperatures and high pressures.