biogas has got the right answer but has missed sumthing. Since particles of gas have more kinetic energy than compared to any other state of matter, its particle move at high speed randomly hence, exerting preasure on the walls of a container.

when molecules of gas moves in the cylinder they collied with the walls or each other they increase the K.E this K.E creats the pressure

A gas is taken into a container (as shown in the given figure). When pressure is applied on the container, the gas particles come closer to each other. This reduces the kinetic energy of the particles. However, the particles are still quite far away from each other, and are still in the gaseous state. When pressure is increased further, the gas particles come very close to each other, and consequently, the gas liquefies.

 ITS exerts pressure because the random movement of particle inside it.

gas molecules move randomly and when they colide with something they exert pressure...... Since particles of gas have more kinetic energy than compared to any other state of matter, its particle move at high speed randomly hence, exerting preasure on the walls of a container.

Why is water a liquid at room temperature?

Water is liquid at room temperature because its boiling point is 100 degree celsius

Gases exert pressure for different reasons like the temperature of the gas and the amount of gas in a container. Other reasons are the size of the container holding the gas or the motion of the molecules found in gases.