Final answer:
Adding gas to a rigid container at constant temperature increases the pressure proportionally to the amount of gas added. Doubling the gas particles doubles the pressure, and tripling them triples the pressure, due to increased collisions with the container walls.
Step-by-step explanation:
When gas is added to an enclosed, rigid container where temperature does not change, the pressure inside the container increases. This happens because the gas particles have the same amount of space in which to move, but there are more particles to collide with the walls of the container. If the amount of gas particles is doubled, the pressure inside the container also doubles, because the gas particles will hit the walls twice as often. Similarly, if the amount of gas particles is tripled, the pressure inside the container will triple.
A rigid container is one that cannot expand or contract, such as a steel canister. According to Avogadro's Law, when the volume of the container is constant and the amount of gas increases, the pressure must also increase proportionally.