Question

A sample of a gas is contained in a closed rigid cylinder. According to kinetic molecular theory, what occurs when the gas inside the cylinder is
heated?
(1) The number of gas molecules increases.
(2) The number of collisions between gas molecules per unit time decreases.
(3) The average velocity of the gas molecules increases.
(4) The volume of the gas decreases.

Answer 1

When a sample of a gas is contained in a closed rigid cylinder and the gas inside the cylinder is heated "(3) The average velocity of the gas molecules increases". The number of molecules stays the same. 

Answer 2

The answer is (3) The average velocity of the gas molecules increases. In the closed rigid cylinder, the volume of the gas and number of gas molecules will not change. The number of collision will increase.