The property of gases mixing easily with each other is called diffusion.

Here's why:

* Diffusion is the spontaneous movement of particles from a region of high concentration to a region of low concentration.

* Gases have a high degree of freedom of movement due to the weak forces between their molecules.

* This allows gas molecules to readily move and intermingle with molecules of other gases, resulting in a homogenous mixture.

Let me know if you'd like to know more about diffusion!