How is a gas different from a liquid?
Liquids have no definite shape, but they have a fixed volume. Their particles are close together but there is a little space between them. This space allows them to move or slide past each other.
On the other hand, a gas has no definite shape and volume; hence, it depends on the shape and volume of the container. It contains particles that are loosely packed. Since there is plenty of empty space, they are able to move freely in all directions.