What is hydration energy ?
@Nitin, Your answer is partially correct. The most precise definition of hydration energy is as follows.
Hydration enthalpy is defined as the amount of energy released when one mole of gaseous ions combine with water to form hydrated ions.
M+ (g) + aq → M+ (aq) + hydration energy
X- (g) + aq → X- (aq) + hydration energy
This hydration energy plays a very crucial role in determining the ionic mobilities of compounds.
Higher the hydration energy of the ions, greater is the solubility of the compound in water. Further, the extent of hydration depends upon the size of the ions. Smaller the size of the ion, more highly it is hydrated and hence greater is its hydrated ionic radius and less is its ionic mobility.
Hope, this helps.