The property of the alkaline earth metals that increases with their atomic number is

 In alkaline earth metals as the atomic number increases the number of atomic orbitals increases. In case of hydroxides, the lattice energies are different because of medium of size of hydroxide ions decreases on moving from Be to Ba. This tend to increase the solubility and to overcome the counter-effect produced by decrease in hydration energy. Hence the solubility of alkaline earth metal hydroxides increases with increase in atomic number.

Whereas electronegativity, Solubility of their sulphates and IE decreases with increase in atomic number.