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Q.
The mean free path of molecules of a gas, (radius $r$) is inversely proportional to
Thermodynamics
Solution:
Mean free path, $\lambda=\frac{1}{\sqrt{2} n \pi d^{2}}$
where $n$ is the number density and $d$ is the diameter of the molecule.
As $d=2 r$
$\therefore \lambda=\frac{1}{4 \sqrt{2} n \pi r^{2}} $
or $\lambda \propto \frac{1}{r^{2}}$