In a gas absorption unit, a $300mo\frac{l}{m}in$ feed gas containing $S{O}_2$ and species $A$ is contacted with fresh water stream that absorbs $S{O}_2.$ The gas stream exit from the top of the absorption unit with total flow rate of $200mo\frac{l}{m}in$ and $5$mol$\%S{O}_2$ in the exit gas stream. It is given that the liquid stream exit from the bottom of the absorption unit with $90$mol$\%$ water in the exit liquid stream. Assume that the absorption of A and evaporation of water in the absorption unit can be neglected. Calculate the absorption efficiency of the absorption unit.