Calculate:
A gas cylinder is filled with hydrogen and it holds 50 g of gas. The same cylinder holds 200 g of gas X and 500 g of gas Y under same temperature and pressure conditions. Calculate the vapour density of gas X and molecular mass of gas Y.

Given,
At same temperature and pressure Mass of hydrogen = 50 g
Mass of gas X = 200 g
Mass of gas Y = 500 g

V.D. of gas X = $\dfrac{\text{mass of certain volume of gas X }}{\text{mass of equal volume of H}_2}$ = $\dfrac{200}{50}$ = 4

V.D. of gas Y = $\dfrac{\text{mass of certain volume of gas Y}}{\text{mass of equal volume of H}_2}$ = $\dfrac{500}{50}$ = 10

Molecular weight = 2 x V.D. = 2 x 10 = 20 a.m.u.

∴ The vapour density of gas X is 4 and Molecular mass of gas Y is 20 a.m.u.