The mean free path 'λ' of a gas molecule, as given by Maxwell, is related to its radius 'a' 

CONCEPT:

• Mean Free Path (λ): The distance travelled by a gas molecule between two successive collisions is known as a free path.
  
• During two successive collisions, a molecule of gas moves in a straight line with constant velocity, and the mean free path of a gas molecule is given by

Where n = number of molecules per unit volume and d = diameter of a molecule

EXPLANATION:

• The mean free path of a gas molecule is given by

As we know, d = 2a, where a = radius of a molecule

• The mean free path of a gas molecule is given by

• Therefore option 1 is correct.

​Additional Information

• From the above, it is clear that the mean free path of a gas molecule depends on the number of molecules per unit volume and diameter of a molecule.