Several reactions of an aqueous solution of compound $X$ are observed. On adding a few drops of aqueous sodium hydroxide, a white precipitate forms. When dilute nitric acid is then added and the mixture is warmed, a gas is produced. This gas decolourises acidified potassium manganate(VII). If dilute nitric acid and aqueous barium nitrate are added, there is no visible change. What can be deduced about the identity of $X$?
- AX contains only aluminium sulfate, $\text{Al}_2(\text{SO}_4)_3$.
- BX contains only calcium sulfite, $\text{CaSO}_3$.
- CX must contain aluminium sulfite, $\text{Al}_2(\text{SO}_3)_3$, or zinc sulfite, $\text{ZnSO}_3$.
- DX must contain aluminium sulfite, $\text{Al}_2(\text{SO}_3)_3$, calcium sulfite, $\text{CaSO}_3$, or zinc sulfite, $\text{ZnSO}_3$.