The vapour density of a gas A is twice that of a gas B. If the molecular weight of B is M, the molecular weight of A will be :

We have
Molar mass= 2 times the vapour density
Mass is given as M. Thus, the value of vapour density,
=$\frac{M}{2}$

Also, given that vapour density of A is four time that of B, th
Thus, the vapour density can be given as,