III$-5.$ A mixture of $75\%H_2$ and $25\%N_2($molar basis$)$ is contained in a tank at $P=800$atm and $T=-70C.$ Estimate the specific volume of the mixture in $1.mo{l}^{-1}$ using Kay's rule

Given :$-$Generalized Compressibility Chart

$-$Critical constants :

$H_2,T_C=41K$;$,P_C=18\mathrm{.}4$atm

$N_2,T_C=126\mathrm{.}2K$;$,P_C=33\mathrm{.}5$atm