Question

The mean free path for gas molecules with molecular diameter $d$ and number density $n$ is proportional to

• A. $\frac{1}{d}$
• B. $d^2$
• C. $\frac{1}{n}$
• D. $\frac{1}{n^2}$

Answer 1

The correct option is C $\frac{1}{n}$

Mean free path of gas molecules is given as
$\lambda =\frac{1}{\sqrt{2}n\pi d^2}$
$\lambda \propto \frac{1}{d^2}$ and $\lambda \propto \frac{1}{n}$