Q.

The mean free path of molecules of a gas, (radius r) is inversely proportional to            [2014]
 

1 r3  
2 r2  
3 r  
4 r  

Ans.

(2)

Mean free path, λ=12nπd2

where n is the number density and d is the diameter of the molecule.

As  d=2r,         λ=142nπr2  or  λ1r2