Question

A gaseous mixture contains 50% helium and 50% methane by volume. What is the percentage by mass of methane in the mixture?

• A. 19.97%
• B. 20.05%
• C. 50%
• D. 80%

Answer 1

The correct option is D 80%

Molar and volume ratio will be same, i.e., 1:1.
$\therefore$ Mass of 1 mole $C{H}_4$ and $He$ will be 16 and 4 g respectively.
Percentage by mass of $C{H}_4$ = $\frac{\text{Mass of}C{H}_4}{\text{Total mass}}\times 100$
$=\frac{16}{20}\times 100=80\%$