Explain why the speed of sound through a gas cannot be greater than the r.m.s. speed of the molecules of the gas.

Explanation

In gases, the molecules move about at random. The oscillations produced by a sound wave are superimposed on this random thermal motion. An impulse given to one molecule is passed on to another molecule after the first one has moved through the empty space between them and collided with the second. The average of the speeds in the space between molecules is the average speed which is close to the rms speed hence the speed of a sound wave can never be greater than the rms speed of the molecules of a gas.