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# A 4:1 molar mixture of He and $CH_4$ is contained in a vessel at 20 bar pressure. Due to a hole in the vessel, the gas mixture leaks out. What is the composition of the mixture effusing out initially?

$(a)\;4:1\qquad(b)\;6:1\qquad(c)\;8:1\qquad(d)\;2:1$

Given
Molar ratio of He and $CH_4$ is 4:1
Partial pressure ratio of He and $CH_4$ is 16:4
$\large\frac{n_{He}}{n_{CH_4}} = \sqrt{\large\frac{M_{CH_4}}{M_{He}}}\times\large\frac{P_{He}}{P_{CH_4}}$
Since total pressure = 20 bar
$= \sqrt{\large\frac{16}{4}}\times\large\frac{16}{4}$
Since time of diffusion for both is same
= 8:1
The composition of mixture initially gone out for He and $CH_4$ is 8:1