Silver nitrate solution is added dropwise to aqueous sodium thiosulphate. The precipitate changes from white to yellow to brown and finally to black. The final black substance and the acid formed in the same step (by hydrolysis) are respectively

1. A$\mathrm{Ag}$ and $\mathrm{SO}{}_3$
2. B$\mathrm{Ag}{}_2\mathrm{S}$ and $\mathrm{H}{}_2\mathrm{SO}{}_4$
3. C$\mathrm{Ag}{}_2\mathrm{O}$ and $\mathrm{SO}{}_2$
4. D$\mathrm{Ag}{}_2\mathrm{SO}{}_4$ and $\mathrm{S}$