Consider the following ionic compounds: CdCO₃, Na₂S, PbSO₄, (NH₄)₃PO₄, and Hg2Cl₂. Which compounds will be soluble when added to water?
1) CdCO₃
2) Na₂S
3) PbSO₄
4) (NH₄)₃PO₄
5) Hg2Cl₂