$4:1$ molar mixture of $He$ and $C{H}_4$ is contained in a vessel at $20$ bar pressure. Due to the hole in the vessel, the gas mixture leaks out.

What is the composition of the mixture effusing out initially?

The molar ratio of He and CH4 is 4:1

The partial pressure ratio of He and CH4 is 16:4

$\frac{n_{He}}{n_{C{H}_4}}=$$\sqrt{\frac{M_{C{H}_4}}{M_{He}}}$$\times \frac{P_{He}}{P_{C{H}_4}}$

Since total pressure = 20 bar

$=\sqrt{\frac{16}{4}}\times \frac{16}{4}$

Since the time of diffusion for both is same

$=8:1$

The composition of mixture initially gone out for He and CH${}_4$ is $8:1$