Give reasons

A) A gas exerts pressure on the walls of the container.

B) A gas fills completely the vessel in which it is kept.

A. In gaseous state the particles move about randomly at high speed. due to this random movement the particles hit each other and also the walls of the container. this force exerted per unit area by the gas particles is called gas pressure.

B. Intermolecular force of attraction in gas is least so the particles can move freely and thus fills completely the vessel in which it is kept.