A gaseous mixture contains 50% helium and 50% methane by volume. What is the percent by weight of methane in the mixture?

Options

A. `19.97%`
B. `20.05%`
C. `50%`
D. `75%`

Explanation

`("Vol. of He")/("Vol. of" CH_(4)) = (50)/(50) = (1)/(1)`
`("No. of molecules of He")/("No. of molecules of" CH_(4))=(1)/(1)`
`("Mass of He")/("Mass of" CH_(4))=(4)/(16)=(1)/(4)`
`:.` Percentage of `CH_(4)` in mixture `(4)/(5)xx100=80%`