Which of the following ions is expected to have maximum hydration energy?

Hydration energy is the amount of energy released when one mole of ions undergoes hydration. Hydration energy is one component in the quantitative analysis of solvation. It is a particular special case of water. The value of hydration energies is one of the most challenging aspects of structural prediction

Be2+ ion has small size and high charge. Hence, it has high polarizing power and can attract several water molecules. Thus it has highest hydration energy among the given ions.

Because of the small size of ${\mathrm{Be}}^{2+}$ions, it will have more hydration energy.