Question

Vapour density of a volatile substance is 4 in comparison to methane ($C{H}_4$ =1). Its molecular mass will be:

• A. 8
• B. 2
• C. 64
• D. 128

Answer 1

The correct option is A 8

Vapour density is the density of vapour in relation to that of Hydrogen.

Vapour density $=\frac{\text{Molar mass of gas}}{2}$

Vapour density $=4$

Then,

$\Rightarrow 4=\frac{\text{Molar mass of gas}}{2}$

$\Rightarrow 8=$ Molar mass of gas