Which of the following will have highest hydration energy?

$\begin{array}{1 1}(a)\;Li^+&(b)\;Na^+\\(c)\;Be^{++}&(d)\;Mg^{++}\end{array}$

Hydration energy depends on charge of ion and ionic radius. Higher the charge, greater the hydration energy. On the other hand, smaller the size, greater the hydration energy.
$Be^{++}$
Due to small in size.
Hence (c) is the correct answer.
edited Mar 25