Q36 / 180 · KCET 2020 · Chemistry

A gas mixture contains $25 \%$ He and $75 \% \mathrm{CH}_{4}$ by volume at a given temperature and pressure. The percentage by mass of methane in the mixture is approximately____

  • A
    $75 \%$
  • B
    $25 \%$
  • Correct answer
    C
    $92 \%$
  • D
    $8 \%$

Solution

Gas mixture contains $25 \%$ He and $75 \% \mathrm{CH}_{4}$ by volumes. We have to calculate the mass percentage of methane in the mixture. molar mass of $\mathrm{He}=4$ molar mass of $\mathrm{CH}_{4}=16$ $\therefore$ Mass percentage of methane in the mixture shall be $=\frac{75 \times 16}{25 \times 4+75 \times 16} \times 100=92 \%$

Hence, the correct answer is option: 'C'.

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