If \( n \) is the number: density and \( d \) is the diameter of the molecule, then the average distance covered by a molecule between two successive collisions (i.e. mean free path) is represented by:
\( \frac{1}{\sqrt{2} n^2 \pi^2 d^2} \)
\( {\sqrt{2} n \pi d^2} \)
\( \frac{1}{\sqrt{2\, n\, \pi\, d^{2}}} \)
\( \frac{1}{\sqrt{2} n \pi d^2} \)