Question

Vapour density of a volatile substance is 4 in comparison to methane (CH₄ = 1). Its molecular weight will be

(a) 8

(b) 12

(c) 64

(d) 128

Answer 1

Correct option is (c) 64

Molecular weight = 2 × Vapour density

\(\frac{M_W}{M_{W_{CH_4}}} = \frac{V.D.}{V.D._{CH_4}} = \frac 41\) (Given)

\(\frac{M_W}{16} = \frac 41\)

⇒ M_W = 64

Hence, the molecular weight of a volatile substance is 64 g/mol.