Because of the open gasoline can filled the garage with the smell of gas

diffusion

Explanation:

Diffusion is the process of movement of particles from high concetration to low concentration.

In the gaseous state of the matter, the molecules are present in irregular pattern. The molecules are not closely packed as they have weak forces of attraction.They can move freely from one place to another and thus move from their high concentration to their low concentration.

Thus due to diffusion, the smell of gas spreads out in open.

ya the other dude is right