A white precipitate is formed on adding $\mathrm{CaCl}{}_2$ solution to a salt solution. It does not dissolve in dilute acetic acid but dissolves in dilute HCl, and the salt decolourises warm acidified $\mathrm{KMnO}{}_4$. The anion is

1. A$\mathrm{SO}{}_4{}^{2-}$
2. B$\mathrm{Cl}{}^{-}$
3. C$\mathrm{C}{}_2\mathrm{O}{}_4{}^{2-}$
4. D$\mathrm{CO}{}_3{}^{2-}$