the number of moles of hydrogen present in a 1,500 mL container at 298 K 1520 mmHG pressure is

since PV/nT is constant, and 1 mole occupies 22.4L at STP, you want n such that

(1520*1500)/(n*298) = (760*22.4)/(1*273)

1 mole= 22.4 Liters at 273 K and 1 atm

1500 mL = 1.5 L
1520 mmHg * 1 atm/ 760 mmHg = 2 atm

P V = n R T
R = P V / nT
1 atm * 22.4 L / 1 mol*273 = 2 atm * 1.5 L /298 n
298 n = 2 * 1.5 * 273 /22.4
n = .123 mols