Ionic mobility of which of the following alkali metal ions is lowest when aqueous solution of their salts are put under an electric field?

Options:

1. Li
2. Na
3. K
4. Rb
5. Among which one is correct option.

The alkali metal ions are highly hydrated. The smaller the size of the ion, the greater is the degree of hydration. The Ionic radius of Li+ is lowest among Li^+, Na^+, K⁺ , Rb^{+ .} Thus, The positive charge density around  Li  ion is quite high due to its very small size. It can attract several layers of aqueous molecules and gets highly hydrated. Thus, Li+ aq  ion is bigger in size compared with other alkali metal ions which are less hydrated. As a result, it moves through the aqueous solution less rapidly compared with ions of other alkali metals under the influence of electric current.