The molar volume is the volume of 1 mol and it is calculated as:
molar Volume = Voumen / number of moles = V / n
Now use the formula pV = nRT, and molar volume = V / n
=> molar volumen = V / n = RT / p
=> V / n = 0.0821 atm*l / K*mol * (21.5 + 273.15)K / 1.00 atm
=> V/n = 24.19 l / mol
Answer: 24.19 l / mol