Diffusion of Gases:
1. The spontaneous mixing of molecules of different gases by random motion and collision until the mixture becomes homogeneous is called diffusion of gases.
2. Molecules of more than one gas are involved.
3. Molecules of lighter gases diffuse fastly.
Effusion of Gases:
1. The escaping of one by one gas molecules without collision through a hole of molecular dimension is called effusion of gases.
2. Molecules of only one gas are involved.
3. Molecules of lighter gases effuse fastly.