Answer
$Mg^{2+}$ ion has larger hydration energy than $Na^{+}$ ion.
Work Step by Step
$Mg^{2+}$ ion has larger hydration energy than $Na^{+}$ ion.
It is the energy released during the bond formation between charged ions and polar water molecules.
The energy released is denoted by a negative sign.
The size of $Mg^{2+}$ ion is small so it has a higher charge density and hence attracts more water molecules. Thus, the $Mg^{2+}$ ion has (higher negative value) larger hydration energy than $Na^{+}$ ion.
