Is gas A oxygen, sulfur dioxide, or dihydrogen sulfide?

Question

Two identical flasks are filled with different gases; both the the flasks are maintained at the same pressure and temperature. The mass of has A is 0.340-g, while the mass of gas B is 0.480-g. Gas B is ozone, O3. Is gas A oxygen, sulfur dioxide or dihydrogen sulfide?

I know that I should probably have to find moles so I divided 0.340g by the molar mass of oxygen, sulfur dioxide, and dihydrogen sulfide, and got...
O=.02124mol
SO2=.0053mol
H2S=.00997mol

I'm really not sure where to go from there

Answer 1

H2S

Identical flasks and same conditions means same volume.
Same volume means they hold same number of mols (assuming ideal gases).
You failed to calc the mols of the given: MW O3 is 48, so known gas is present as 0.01 (approx) mols (0.480 / 48)
This equates to H2S

Answer 2

Its really easier than you think. SInce the flasks are identical (same volume) and are at the same temp. and pressure, the moles of gas in the 2 flasks must be the same. PV=nRT

Since flask A has fewer grams than flask B, Gas A must have a lower molecular mass than Ozone (O3). The only possible choice is Oxygen (O2). The other gases are heavier. You can quantitatively prove your anser as well. The molar mass of O2 is 2/3 compared to the molar mass of O3. This ratio matches the data in your problem as well.