Why it LiF almost insoluble in water while LiCl is soluble not only in water but also in acetone ?

Explanation

Both `Li^+` and `F^(-)` ions have small size and therefore, LiF has high lattice energy. Although the hydration energy of LiF is also high but, it is less than lattice energy (hydration energy of LiF = -1034 kJ, lattice energy = -1045 kJ). Therefore, it is insoluble.
On the other hand, all other alkali metal fluorides have lower lattice energies than corresponding hydration energies and therefore, these are soluble.