The pressure exerted by a gas is due to the random motion of particles in the gas. Gases have weak intermolecular forces and the particles in continuous random motion and these particles collide with the walls of the container. These collisions with the walls of the container exerts pressure on the gas.
Gas pressure is caused when gas particles hit the walls of their container. The more often the particles hit the walls, and the faster they are moving when they do this, the higher the pressure.
