Question

The mean free path of molecules of a gas, (radius '$r$') is inversely proportional to

• A. $r^3$
• B. $r^2$
• C. $r$
• D. $\sqrt{r}$

Answer 1

The correct option is B $r^2$

Formula for Mean free path is
$\lambda =\frac{1}{\sqrt{2}\pi d^{2}n}$
Using $d=2r$
$\lambda =\frac{1}{4\sqrt{2}\pi r^{2}n}$
$\lambda \propto \frac{1}{r^2}$