1. Its barium salt is insoluble in water, but its copper salt is soluble
2. Its copper salt is insoluble in water, but its sodium salt is soluble.
3. Its mercury (II) salt is soluble in water, but its mercury (I) salt is insoluble.
Don't 2 and 3 have multiple answers? I think I'm only supposed to have one, though? How do you differentiate using the water solubility chart?