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

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: