Q: A chemist is studying one of the five oxides of nitrogen: N2O, NO, N2O3, NO2, or N2O5. He learns that 250mL of the gas has a mass of 0.335g. Which oxide is he working with? To get an answer, I would first calculate the mL of each substance, but how? I only know that one mol=22.4mL at STP, but I don't think these are at STP. Plz help.