Gas pressure is caused by the particles colliding with the walls, applying a force to them. It is related to the rate of particle-wall collisions per unit surface area of the container per unit time.
A is incorrect because with an increased number of particles more particle-wall collisions will occur and that will lead to a greater rate of collision per unit surface area of cylinder per unit time since there will be no change in the speed of the particles.
B is incorrect because actually the additional particles bring in more kinetic energy so the existing kinetic energy is not being distributed over a larger number of particles. Additionally, since the temperature is being kept constant, the average kinetic energy is constant.
C is correct because there are now more particles in the same volume, the rate of collision per unit surface area of the cylinder per unit time will increase.
D is incorrect because there is no change in the average speed of the particles due to the temperature remaining the same. Temperature is related to the average kinetic energy of the particles, and the particle kinetic energy depends on the speed of the particles.
