The escape speed of gases on the surface of Moon is much less than the root mean square speeds of gases due to low gravity. Due to this all the gases escape from the surface of the Moon.

Law of equipartition energy states that the average kinetic energy of system of molecules in thermal equilibrium at temperature T is uniformly distributed to all degrees of freedom (x or y or z) directions of motion so that each degree of freedom will get \(\frac{1}{2}\)kT of energy.

Relation between the average kinetic energy and pressure is
\(\mathrm{P}=P=\frac{2}{3} K . E\)
P - Pressure
K.E - kinetic energy

We get \(P V=\frac{2}{3} U\) For a fixed pressure, the volume of the gas is proportional to internal energy of the gas or average kinetic energy of the gas and the average kinetic energy is directly proportional to absolute temperature. It implies that.
\(\mathrm{V} \propto \mathrm{T} \text { or }  \)
\(\frac{V}{T}=\text { constant }\)
This is Charles' law

This law states that at constant temperature and pressure, equal volumes of all gases contain same number of molecules. For two different gases at the same temperature and pressure, according to kinetic theory of gases. We get
\(\mathrm{P}=\frac{1}{3} n m \overline{v^{2}} \ or \ \mathrm{P}=\frac{1}{3} \frac{N}{V} m \overline{v^{2}}\)
\(\mathrm{P}=\frac{1}{3} \frac{N_{1}}{V} m_{1} v_{1}^{2} \)
\(=\frac{1}{3} \frac{N_{2}}{V} m_{2} v_{2}^{2}\)   ......(1)
where \(\overline{v_{1}^{2}} \ and \ \overline{v_{2}^{2}}\) are the mean square speed for two gases and \(\mathrm{N}_{1} \ and \ \mathrm{N}_{2}\) are the number of gas molecules in two different gases.
At the same temperature, average kinetic energy per molecule is the same for two gases.
\(\frac{1}{2} m_{1} \overline{v_{1}^{2}}=\frac{1}{2} m_{2} \overline{v_{2}^{2}}\)   ........(2)
Dividing the equation (1) by (2) we get
N₁ = N₂