$Q$#$2$

A gas$-$gas separation membrane process was used to remove the argon from a mixture of gases $($Argon$,$ Nitrogen and Oxygen$)$ with a molar fraction of $0\mathrm{.}05\%Ar$ and $20\%$ of $O_2.$ The permeate has a following composition $0\mathrm{.}01Ar$ and $25\%O_2$

a$)$ Determine the mol. fraction ${}_{A\frac{r}{N_2}+O_2}$ and the permeate mixture.

b$)$ Calculate the selectivity of the membrane for the Ar related to the combined solvents $(O_2+N_2)$ and discuss the result