Which of the following alkali metal salts is the most soluble in water: $\text{LiF}$, $\text{LiCl}$, $\text{LiBr}$, or $\text{LiI}$?

Solution

1. The solubility of ionic compounds depends on the balance between lattice energy and hydration energy.
2. For lithium halides, the lattice energy decreases significantly as the size of the halide ion increases from ${\text{F}}^{-}$ to ${\text{I}}^{-}$.
3. The large size of the ${\text{I}}^{-}$ ion leads to a lower lattice energy compared to the hydration energy released upon dissolution.
4. Hence the answer is (D).