If a gas has a pressure of 50.0 mm Hg at 540 K what will be the pressure at 200K if the volume does not change?

If you dcrease the temperature you will decrease the pressure proportionately. So, T1 over T2 will equal P1 over P2. We can derive the formula P1 x T2 = P2 x T1. Substitue the values and we get 50.0 mm x 200K = P2 x 540K 10,000 mmK = P2 x 540K 10,000mmK / 540K = P2 P2 = 18.52 mm of Mercury in a constant volume