Calculate mass % of He in a mixture of `O_(2)` and He gas at 3 atm and `27^(@)C` havin density `(5)/(3)` gm/litre [Take : R=0.08 atm litre `mol^(-1)k^(-1)`]

Explanation

PM=dRT for mixture
`3xxM_("avg")=((5)/(3))xx0.08xx300`
`M_("avg")=(5xx8xx3)/(3xx3)=(40)/(3)`
`M_("avg")=(100)/((x)/(4)+(100-x)/(32))=(40)/(3)rArr(100xx32xx4)/(32x+400-4x)=(40)/(3)`
`32xx10xx3=28x+400`
`=28x=960-400=560`
x=20%
`(20)/(10)=2`