Lithium salts are mostly hydrated because

Lithium salts are mostly hydrated due to the following reasons:

1. Smaller atomic size of lithium: Lithium has the smallest atomic size among the alkali metals, which leads to a highly concentrated charge on the lithium ion. This makes lithium ions attract water molecules more strongly, leading to hydration.
2. Higher enthalpy of ionization of lithium: Lithium requires more energy to lose its electron compared to other alkali metals. This high enthalpy of ionization means that lithium ions are more stable when surrounded by water molecules.
3. Maximum degree of hydration of lithium ion: Due to the small size and high charge density, lithium ions can form a larger number of bonds with water molecules, resulting in a higher degree of hydration.

So, all these factors contribute to lithium salts being highly hydrated.