500 mL 500 mL
2 g $H_2 $ 16 g $CH_4$
$PH_2$ $P_{CH4}$
$P = \frac{nRT}{V} = \frac{m\,RT}{MV}$
($m$ = mass of gas, M = Molecular mass)
$P_{H_2} = \frac{2 \, RT}{2 \times 500} = \frac{RT}{500}$ = P (given)
$P_{CH_4} = \frac{16 \, RT}{16 \times 500} = \frac{RT}{500} = P_{H_2} = P$
Partial pressure of $H_2$
$P_{H_2} = \frac{2 \times RT}{2 \times 1000} = \frac{RT}{1000} = \frac{P}{2}$
Partial pressure of $CH_4$
$P_{CH_4} =\frac{16 \times RT}{16 \times 1000} = \frac{RT}{1000} = \frac{P}{2}$
$P_{Total} = P_{H_2} + P_{CH_4} $= P/2 + P/2 = I