Question

A gaseous mixture contains $70\%N_2$ and a $30\%$ unknown gas, by volume. If the average molecular weight of gaseous mixture is $37.60$, the molecular weight of unknown gas is:

• A. $42.2$
• B. $60$
• C. $40$
• D. $50$

Answer 1

The correct option is B $60$

Average $M.M=\frac{\sum \%abundance\times M.M}{\sum \%abundance}$

$\therefore 37.60=\frac{0.70\times 28+0.30\times M_{unknown}}{0.70+0.30}$

$\frac{37.60-19.60}{0.30}=M_{unknown}$

$\therefore M_{unknown}=60gm$

Hence, option $B$ is correct.