A 500 Liter volume of Helium gas is at a pressure of 750 mm Hg...

a 500 Liter volume of Helium gas is at a pressure of 750 mm Hg and has a temp of 300K. What is the Volume of the same gas at standard temperature and pressure (STP)?

At STP, pressure is 1 atm or 760 mmHg, and the temperature is 273 K.

Combined Gas Law:
P1V1 / T1 = P2V2 / T2

Let V2 be the new volume of He gas.
P1V1T2 / T1 = P2V2
P1V1T2 / P2T1 = V2
(750 mmHg)(500 L)(273 K) / (760 mmHg)(300 K) = V2
449.01 L = V2 (Answer)

Have a good day.