c
The mean free depends on diameter of. molecule,
The mean free path or average distance between collisions of a gas molecule may be estimated Erom kinatic Energy.
It depend on tomperature, pressure as wellas Diameter.
$\lambda=\frac{k T}{\sqrt{2} d^{2} p}$
According to mean free path formular,
$\text { path } \propto \frac{1}{d^{2}}$
$\Rightarrow \lambda \propto d^{-2}$
Thus. The mean path of gas molecule $\propto d^{-2}$
Option $(c)$ is correct.