The mixing of different gases by random molecular motion with frequent collisions is called

Diffusion

Explanation:

Diffusion can be defined as the mixing of different gases by random molecular motion and with frequent collisions.

It is a process whereby gas particles move from an area of higher concentration to an area of lower concentration due to constant random motion.

This would cause the gases to mix up gradually  and then form an homogeneous mixture.

explanation:

considering the bohr theory, the type of connection that requires the transfer the answer conuldn't be right