A sample of argon gas is sealed in a container. The volume of the container is doubled. If the pressure remains constant, what happens to the absolute temperature?

This question relates to the combined gas law: P1V1/T1 = P2V2/T2. Since the pressure remains constant, the pressures may be removed from the combined gas law to produce Charles's law: V1/T1 = V2/T2. This equation may be rearranged to: T2 = V2T1/V1. The doubling of the volume means V2 = 2 V1. On substituting: T2 = 2V1T1/V1; giving T2 = 2T1. The identity of the gas is irrelevant in this problem.