Question

The density of a gas 'A' is three times that of a gas 'B'. If the molecular mass of 'A' is $M$, the molecular mass of 'B' is:

• A. $3M$
• B. $M/3$
• C. $\sqrt{3}M$
• D. $\frac{M}{\sqrt{3}}$

Answer 1

The correct option is B $M/3$

The density of a gas 'A' is three times that of a gas 'B'. If the molecular mass of 'A' is $M$, the molecular mass of 'B' is $M/3$.

$PM=dRT$

Hence, the molecular mass is directly proportional to density.

$\frac{M_B}{M_A}=\frac{d_B}{d_A}=\frac{1}{3}$ (as density of a gas 'A' is three times that of a gas 'B')

$M_B=\frac{M_A}{3}$

Hence, option $B$ is correct.