In the hydrated lithium ion the number of water molecules surrounding each lithium ion in its primary layer is $\mathrm{\_\_\_\_}$
 

Lithium ion and its compounds are heavily hydrated due to small size of Li ⁺ ion and it easily polarizes the water molecules than other alkali metals.

the Li ⁺ ion is mainly bonded to 4 water molecules, located at a distance in between 1.99 and 2.11 Å. The geometry of Li ⁺ , hydrated by these 4 water molecules tetrahedrally.