Give the definition for diffusion. gas molecules mix unequally gas molecules spread out in a concentration gradient gas molecules mix equally average distance between collisions gas molecules escape from a container into a vacuum through a small hole

Gas molecules spread out in a concentration gradient.

Explanation:

The correct option is

Gas molecules spread out in a concentration gradient.

Diffusion can be defined as the net passive moment of particles (atoms, ions, molecules) from a region where their concentration is higher to the region where their concentration is less. The process is continued till the concentration of particles are equal on both the regions.

For examples the noxious smell of ammonia spreading in air.