Explanation

(d) $\gamma_{mixture} = \frac{\frac{\mu_{1}\gamma_{1}}{\gamma_{1} - 1} + \frac{\mu_{2}\gamma_{2}}{\gamma_{2} - 1}}{\frac{\mu_{1}}{\gamma_{1} - 1} + \frac{\mu_{2}}{\gamma_{2} - 1}}$
$\mu_{1} =$ moles of helium $= \frac{16}{4} = 4$
$\mu_{2} =$ moles of oxygen $= \frac{16}{32} = \frac{1}{2}$
$\Rightarrow \gamma_{mix} = \frac{\frac{4 \times 5/3}{\frac{5}{3} - 1} + \frac{1/2 \times 7/5}{\frac{7}{5} - 1}}{\frac{4}{\frac{5}{3} - 1} + \frac{1/2}{\frac{7}{5} - 1}} = 1.62$