Property of the alkaline earth metals that increases with their atomic number is:

As the atomic number increases, the number of atomic orbital in alkaline earth metals. The lattice energies for hydroxides differ because the mean size of the hydroxide ions shrinks as they transition from Be to Ba. This tends to improve solubility and neutralize the negative effects of the loss of hydration energy. Thus, as the atomic number grows, alkaline earth metal hydroxides become more soluble.