Hint :We know that the hydrated radius is defined as the radius of ions and closely bonded water molecules. It is inversely related to the atomic radius of an element. As atomic size decreases, hydrated radius increases and vice-versa. This means that as the ionic size decreases, its hydrated radius increases.
Complete Step By Step Answer: We know the hydrated radius is defined as the radius of ions and closely bonded water molecules. This means that the hydrated radius is the radius of ions when surrounded by water molecules. The energy released when an ion is hydrated i.e. accepts water molecules is known as hydration energy. Smaller ion in size accepts a large number of water molecules so its hydration energy is more and greater than its hydrated radius and vice versa. The ionic size decreases along a period and the ionic / atomic size decreases down a group. This means that along a period hydrated radius increases and down a group hydrated radius decreases. Also hydrated radius is defined as the radius of ions and closely bound water molecules. The ions with bigger size and low charge hold water molecules less tightly and thus have smaller atomic radius.
Additional Information: Hydrated radius for elements in a group. We know that size increases down a group as additional shells are being added up. This leads to decrease in the Hydrated radius because the two are inversely proportional to each other. So, we can say that the topmost element would have the smallest size and the highest Hydrated radius. Now, we know that ionic mobility is related to the ease or speed with which an ion can move in a solution. We can add to this that highly solvated ions have a large number of solvent molecules around them and thus have less mobility. So, Hydrated radius is inversely proportional to the ionic mobility as well.
Note : Remember that the smaller is the atomic size of the atom, more will be its hydrated radius and more will be its hydration energy (the amount of energy liberated when an ion accepts a water molecule or we can say when an ion gets hydrated).