Which of the following correctly describes molecules of two different gases if they are at the same temperature and pressure?

A. They must have the same mass

B. They must have the same velocity

C. They must have the same average kinetic energy

D. They must have the same average potential energy

Option C = They must have same average kinetic energy.

Explanation:

According to the kinetic molecular theory,

1. The kinetic energy of gas molecules is only depend upon the temperature.

2. The gas molecules are randomly moves in any direction and thus colloid with each other and wall of container. This collision is elastic.

3. The volume of gas particles is negligible as compared to the volume of container.

4. The ideal gas does not exhibit attractive and repulsive forces.

The first postulate of kinetic molecular theory state that the average kinetic energy is depend upon the temperature so at the same temperature and pressure the two different gases have same kinetic energy.