A gas cylinder is filled with 0.50 mol of N₂(g) and 1.00 mol of O₂(g) at a total pressure of 750 torr. Assuming ideal-gas behavior and constant temperature and volume, what is the partial pressure of O₂ in the cylinder?
a) 525 torr
b) 375 torr
c) 500 torr
d) 250 torr