Chemistry - Salt Analysis Question with Solution | TestHub

The anion forms a white precipitate with silver nitrate ($AgN{O}_3$), lead acetate ($Pb(C{H}_{3}COO{)}_2$), and barium hydroxide ($Ba(OH{)}_2$). Crucially, it shows no precipitate with calcium hydroxide ($Ca(OH{)}_2$), indicating that its calcium salt is soluble in water. Among the options, $C{O}_3^{2-}$, $S{O}_3^{2-}$, and $C{l}^{-}$ all form insoluble calcium salts or different reaction patterns; however, thiosulfate ($S_2{O}_3^{2-}$) fits this profile as calcium thiosulfate is soluble. Therefore, the anion in the aqueous solution is $S_2{O}_3^{2-}$, making (D) the correct answer.