why do the solubilities differ in lead and alkaline earth metal compounds?

Question

"As you have seen, lead can form the same kinds of compounds as the alkaline earth metals. Nevertheless, the solubilities may differ markedly. Give a convincing reason"

Answer 1

The lead compounds would be much more covalent in character, with a very high bond strength (aka lattice enthalpy). Where a compound is insoluble, this energy is too high for hydration enthalpies (the energy released when water surrounds an ion of either charge) to compensate for.