Vapour density of hydrocarbon = 8
∴ Molecular weight = 2 × Vapour density
= 2 × 8 = 16 g
16 g of hydrocarbon at s.t.p. occupy 22.4 lit
∴ 40 g of hydrocarbon will occupy = 22.4\over16 × 40
= 56 lit
Hence, volume occupied by 40 g of a hydrocarbon (CH4) at s.t.p. is 56 lit.