An acidified solution of $0.05 \,M\, Zn ^{2+}$ is saturated with $0.1 \,M \,H _{2} S$. What is the minimum molar concentration $(M)$ of $H ^{+}$required to prevent the precipitation of $ZnS$ ? Use $K_{s p}( ZnS )=1.25 \times 10^{-22}$ and overall dissociation constant of $H _{2} S. K _{ NET }=K_{1} K_{2}=1 \times 10^{-21}$