`50 mL` of each gas `A` and of gas `B` takes `150 and 200` seconds respectively for effusing through a pin hole under the similar conditon. If molecular mass of gas `B` is `36`, then the molecular mass of gas `A` will be

Options

A. 95
B. 128
C. 20
D. 64

Answer

C

Explanation

`r_(A) = (V_(A))/(t_(A)) = 50/150`
`r_(B) = (V_(B))/(t_(B)) = 50/200`
According to Graham's Law of effusion
`(r_(A))/(r_(B)) = sqrt( M_(B))/(M_(A))`
`(200)/(150) = sqrt((36)/(M_(A))` or `M_(A) = (36 xx 150 xx 150)/(200 xx 200)`
`M_(B) = 2.25 ~~ 20`.