We assume it as an ideal gas therefore we can use the
ideal gas equation to solve the problem. The ideal gas equation is expressed as
PV = nRT. We are given the volume, temperature and pressure. Therefore, we can solve for the amount of the gas in moles.
n = PV / RT
n = 1.00(3L) / (0.08206 atm L/mol K ) 273 K
n = 0.1339 mol