Q9. 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 :\\
(1) $\sqrt { 2 } n \pi d ^ { 2 }$\\
(2) $\frac { 1 } { \sqrt { 2 n \pi d ^ { 2 } } }$\\
(3) $\frac { 1 } { \sqrt { 2 } n \pi d ^ { 2 } }$\\
(4) $\frac { 1 } { \sqrt { 2 } n ^ { 2 } \pi ^ { 2 } d ^ { 2 } }$