Hydrogen sulfide is bubbled into $0.20\mathrm{M}$ $\mathrm{HCl}$ until $[\mathrm{H}{}_2\mathrm{S}]=0.10\mathrm{M}$. Taking $[\mathrm{H}{}^{+}]=0.20\mathrm{M}$ and $K_{a1}{K}_{a2}=1.0\times 10^{-21}$, the concentration of $\mathrm{S}{}^{2-}$ is

1. A$5.0\times 10^{-22}\mathrm{M}$
2. B$1.0\times 10^{-22}\mathrm{M}$
3. C$2.5\times 10^{-20}\mathrm{M}$
4. D$2.5\times 10^{-21}\mathrm{M}$