The solubility of metal halides depends on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluroides of alkali metals, the lowest solubility of LiF in water is due to

As with increases of cation size lattice energy decreases and hence solubility increasesGenerally in a series with increase the size of oppositely charged in lattice enthalpy decreasesIn case of , [smaller size anions]If the anion size is small, then with small change in cation size, there is a considerable change in lattice energy and not depends on the hydration energy LiF is least soluble (or) insoluble,because its lattice is very high, and From LiF to CsF solubility increases i.e., CsF is highly soluble