what volume is occupied by 25 g of oxygen gas at a pressure of 733 mmhg and a temperature of 30.5 degrees?

Molar mass of O2 = 16×2 = 32 g/mol

Number of moles, n = (25/32) mol
Pressure, P = (733/760) atm
Temperature, T = (273 + 30.5) K
Gas constant, R = 0.0821 atm L/(mol K)

PV = nRT
(730/760) V = (25/32) × 0.0821 × (273 + 30.5)
V = (25/32) × 0.0821 × (273 + 30.5) × (760/730)
Volume, V = 20.3 L

Use the Ideal Gas Eq'n
PV = nRT
or
V = nRT/P

Convert terms
V to be found will be in cubic metres (m^3)
n = number of moles ( = 25g/32)
R = Gas constant 8.314
T = temperature in Kelvin ( 30.5 + 273 = 303.5K )
P = Pressure in Pascals ( (733/760) x 101325 = 97725.296 Pa)

Substituting in
V(m^3) = (25/32) x 8.314 X 303.5 / 97725.296
V(m^3) = 0.020172 m^3
V = 20.172 dm^3 ( litres).