Kinetic Molecular Theory of Gases:

Kinetic Theory of gases says that all gases consists of molecules. All molecules of a particular gas are similar. It is experimentally proven that a gas at standard conditions consists 3 x 10²⁵ molecules per cubic meter. The distances between molecules in gases are very large as compared to dimension of the molecules.

Molecules of gas move in random directions, and they collide with one another and with the walls of the container, these collision are perfectly elastic. Molecules of gases are essentially neutral i,e; they have no charge due to which there is no electric force among them, also due to very small masses gravitational forces among them are also very negligible. So they move freely in straight paths but in random directions.