Question

Which one of the following is most covalent in nature among lithium halide?

• A. LiF
• B. LiCl
• C. LiBr
• D. LiI

Answer 1

The correct option is D LiI

The $L{i}^{+}$ ion is very small in size and has high tendency to distort electron cloud around the negative Iodide ion.
Due to large anionic size among other halides, polarizability of iodide ion is higher
and thus has highest covalent character
Lithium iodide is most covalent in nature among lithium halide.

Theory
Reactivity towards halogen:
Alkali metals readily react vigorously with halogens to form ionic halides,$M^{+}{X}^{-}$
$2M+X_2⟶2M^{+}{X}^{-}$

Lithium halides are somewhat covalent because of the high polarization capability of lithium ion.
Since anions with larger size can be easily distorted, Lithium iodide is the most covalent in nature.

Characteristics:
High melting colorless crystalline solids
${\Delta }_{r}H$ always becomes less negative from fluoride to iodide.
Melting and boiling point:
fluoride > chloride > bromide > iodide
All these halides are soluble in water.
Low solubility in water:
LiF - High lattice enthalpy
CsF - Small hydration enthalpy
Other halides of lithium are soluble in ethanol, acetone and ethyl acetate. LiCl is soluble in pyridine too.