Henry’s law constant for the molality of methane in benzene at 298 K is

Here,

p = 760 mm Hg

kH = 4.27 × 105 mm Hg

According to Henry’s law,

p = kHx

$\Rightarrow x=\frac{p}{k_{\mathrm{H}}}$

$=\frac{760 \mathrm{~mm} \mathrm{Hg}}{4.27 \times 10^{5} \mathrm{~mm} \mathrm{Hg}}$

= 177.99 × 10−5

= 178 × 10−5 (approximately)

Hence, the mole fraction of methane in benzene is 178 × 10−5.