When aqueous sodium hydroxide is added to an aqueous solution of compound Y, a green precipitate is formed. Aqueous ammonia likewise gives a green precipitate when it is added to an aqueous solution of compound Y. In both tests, the precipitate remains insoluble if excess reagent is added. Which ion must be contained in Y?
- Achromium(III)
- Bcopper(II)
- Ciron(II)
- Diron(III)