A rigid container contains some ideal gas. Mean free path of the molecules is $\lambda$. If temperature of the gas is now doubled, mean free path of the molecules will be 

Mean free path $\lambda =\frac{1}{\sqrt{2}\pi d^{2}x}$

where d= diameter of molecule 

and n = Number of molecules per unit volume.

Since the volume of the container remains uncharged, ‘n’ remains unchanged and hence mean free path remains unchanged.