Chemistry · Oct / Nov 2023 · Paper 12 · Question 40

The results of some tests on polluted river water are shown. | reagent | observation on adding reagent slowly | observation on adding excess reagent | |---|---|---| | aqueous sodium hydroxide | white precipitate | precipitate dissolves to give a colourless solution | | aqueous ammonia | white precipitate | no further change | Which metal ion must be present in the water?

1. AAl$^{3+}$
2. BCa$^{2+}$
3. CFe$^{2+}$
4. DZn$^{2+}$

As printed in the paper