$\Rightarrow r_{1}=r_{2}$

$\Rightarrow \frac{P_{ I }}{\sqrt{T_{ I }}}=\frac{P_{ II }}{\sqrt{T_{ II }}}$

Now, mean free path of a gas molecule is

or $\quad \lambda \propto \frac{T}{P}$

So, $\quad \frac{\lambda_{ I }}{\lambda_{ II }}=\frac{T_{ I } / P_{ I }}{T_{ II } / P_{ II }}$

$=\frac{T_{ I }}{T_{ II }} \times \frac{P_{ II }}{P_{ I }}=\frac{T_{ I }}{T_{ II }} \times \frac{\sqrt{T_{ II }}}{\sqrt{T_{ I }}}$

$\Rightarrow \quad \frac{\lambda_{ I }}{\lambda_{\text {II }}}=\frac{\sqrt{T_{ I }}}{\sqrt{T_{ II }}}=\sqrt{\frac{150}{300}}$

$\Rightarrow \quad \frac{\lambda_{ I }}{\lambda_{ II }}=0.7$