Density of water vapour at room temp. and 1 atm. pressure is given to be .737 g/L.Compound A is 80.0% carbon by mass and 20% hydrogen.Compund B is 83.3% carbon by mass and 16.7% hydrogen.Density of gaseous Compound A is 1.227 g/L,and the density of Compound B is 2.948 g/L.Show how these data can be used to calculate the molar massess of Compound A and Compund B assuming that the molar mass of water is 18.

For compound A, we know that it is made up of carbon and hydrogen only and we also know their mass% .
So we can get the mole % of C and H in the compound A. From this we know the molar ratio of the C &H in the compound and we can gat empirical formula.
Now as 1 mole of each of the gas will occupy 24.4 litre at room temp. So 1L wiould contain 1/24.4 L. Ande the mass is given for 1L.
So we can get molecular weight using formula: mole=mass/Molecular-weight
Noe we can also know the molecular formula of the compond if We have got molecular weight and empirical formula. Similarly for Compound B.