Correct Answer - `8 : 1`
Partial pressure ratio of `He " and " CH_(4) " is " 16 : 4`
For diffusion `(r_(He))/(r_(CH_(4))) = sqrt((M_(CH_(4)))/(M_(He))) xx (p_(He))/(p_(CH_(4)))`
`(n_(He))/(n_(CH_(4))) = sqrt((16)/(4)) xx (16)/(4) = 8`
i.e., mole ratio of diffusion for He and `CH_(4) " is " 8 : 1`