Question

Why gas can fill the whole container in which it is enclosed?

Answer 1

Because of the characteristic of matter that particles of it are moving constantly. Gas expands which creates pressure on the walls of the container.

Answer 2

Gas can fill the in whole container which it is enclosed as the intermolecular force of attraction in gas is very weak . Thus the particles can move here and there in random motion as they can easily overcome the intermolecular force of attraction . Thus the fill up the whole container.