Kinetic Theory of Gases: Practice Problem & Solution

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Kinetic Theory of Gases. Understanding the underlying formula is key to arriving at the correct answer below:

The mean free path is given by $\lambda = \frac{1}{\sqrt{2}\pi n d^2}$. Since molecular diameter $d = 2r$, we have $\lambda \propto \frac{1}{d^2} \propto \frac{1}{r^2}$. Therefore, it is inversely proportional to $r^2$.