The mean free path for a gas, with molecular diameter \(d\) and number density \(n,\) can be expressed as:
1. $\frac{1}{\sqrt{2}n{\mathrm{\pi d}}^2}$
2. $\frac{1}{\sqrt{2}{n}^2{\mathrm{\pi d}}^2}$
3. $\frac{1}{\sqrt{2}{n}^2{\pi }^2{d}^2}$
4. $\frac{1}{\sqrt{2}n\mathrm{\pi d}}$

If the mean free path of atoms is doubled , then the pressure of the gas will become:

1. P/4                       

2. P/2

3. P/8                       

4. P

If the pressure in a closed vessel is reduced by drawing out some gas, the mean free path of the molecules: