Q.

The number of air molecules per cm3 increased from 3×1019 to 12×1019. The ratio of collision frequency of air molecules before and after the increase in number respectively is           [2023]

1 0.75  
2 0.50  
3 0.25  
4 1.25  

Ans.

(3)

Collision frequency,

f=Vλ=V(12πd2nv)=2πd2vnv

  fn, nv is number density

f1f2=nv1nv2=3×101912×1019=0.25