Since at STP, the molar volume is 22.4 L, all of these containers have one mole of gas. The one with the highest atomic or molecular weight is the heaviest: : A) H2 - 2 g/mole B) N2 - 28 g/mole C) O2 - 32 g/mole D) CO2 - 44 g/mole E)He - 4 g/mole Ans will CO2 - 44 g/mole with the highest atomic or molecular weight is the heaviest.