Trials were performed on an aqueous solution of an unidentified compound, $P$. The observations are shown in the table. Aqueous sodium hydroxide added: green precipitate, soluble in excess to give a green solution. Dilute nitric acid added, followed by aqueous barium nitrate: white precipitate. Dilute nitric acid added, followed by aqueous silver nitrate: no precipitate. Which ions are present in $P$?
- A$\text{Cr}^{3+}$ and $\text{Cl}^-$
- B$\text{Cr}^{3+}$ and $\text{SO}_4^{2-}$
- C$\text{Fe}^{2+}$ and $\text{Cl}^-$
- D$\text{Fe}^{2+}$ and $\text{SO}_4^{2-}$