A mixture of `O_(2)` and gas ''Y'' (mol. Mass 80) in the moe ratio a: b has a mean molecular mass 40. What would be mean molecular mass , if the gases are mixed in the ratio b: a under identical conditions? ( Assume that gases are non- reacting ):

Options

A. 40
B. 48
C. 62
D. 72

Answer

4

Explanation

Let mole fraction of `O_(2)` is `x`
`40=32xx x+80(1-x)" "`or `" " x=5//6`
`a+b=x:(1-x)=(5)/(6):(1)/(6)`
When ratio is changed
`M_("mixture")=32xx(1)/(6)+80xx(1)/(6)=72`