Question

molar volume of o2

Answer 1

Would this be at STP by any chance? If so, STP = 1atm and 0C.
If an amount of mole was not specified, I would assume it is talking about 1 mole of O2. The molar volume of ANY gas at STP is 22.4 L.

This can be proven here:
Converting to Kelvin: 273.15K + 0C = 273.15K
You would want to use the ideal gas law here.

PV = nRT
(1)(V) = (1 mol gas)(0.08206 L*atm/mol*K)(273.15K)
V = 22.4 L

Answer 2

the molar volume of any gas at STP is always 22.4L, as @miyagii says. because there is so much space between gas molecules, the \(identity\) of the gas isn't important, just the number of molecules that are colliding with the walls, creating 1atm of pressure (at STP).