Gases exert pressure on the walls of the container because the gas molecules
A. have finite volume
B. obey Boyle’s law
C. possess momentum
D. collide with one another

Hint: At a given temperature, molecules of a gas possess thermal energy. Therefore, the molecules are in random motion. Due to this motion, the molecules collide with the walls of the container and exert a force on the walls. Thus, a pressure is exerted on the walls.

Complete step by step answer:
A gas is made up of many numbers of molecules. These molecules possess a finite mass.
According to the kinetic theory of gases, at a given temperature the molecules of the gas possess some energy called thermal energy. Due to this energy, the molecules are in continuous motion. However, the molecules do not move in a specific path or specific direction. Hence, every molecule of the gas travels in a random direction.
Since the molecules are in motion and have a definite mass, they possess some momentum. When a gas is placed inside a container, due to the random motion of the molecules, the molecules collide with each other and they also collide with the walls of the container.
When a molecule collides with the wall of the container, the wall exerts a force on the wall that changes the direction of motion of the molecule. In return, the molecules also exert a force on the wall. Similarly, all the molecules randomly collide with the walls of the container and as a result, a net force is applied on the wall.
When we divide the perpendicular force to the wall with the area of the wall, we get the pressure exerted on the wall by the molecules of the gas. This is possible because the molecules have a momentum. If they were at rest, then there would not be any pressure on the walls of the container.
Hence, the correct option is C.

Note: When a gas is placed inside a container, it occupies a volume equal to the volume of the container because a gas does not have a fixed shape and size and it is compressible too.
When a gas obeys Boyle’s law, the pressure of the gas is directly proportional to the volume of the gas at a constant temperature.
There is a pressure on the walls because the molecules collide with walls and not because of the molecules colliding with each other.