The empirical formula of an organic compound carbon & hydrogen is `CH_(2)` The mass of `1"litre"` of organic gas is exactly equal to mass of 1 litre `N_(2)` therefore molecular formula of organic gas is .

Explanation

Empirical Mass of `CH_(3)=12+2=14`
`because` Mass of 1 litre of organic gas = Mass of 1 litre of `N_(2)`
Since V,P,T, n are same.
Therefore PV=`(m)/(M)RT`
implies that molar mass should also be same.
`therefore ` Molecular mass of organic compound will be 28 g
`n=("Molecular mass")/("Empirical mass")=(28)/(14)=2`
So molecular formula `=2xxCH_(2) =C_(2)H_(4)`