The solubility of metal halides depends on their nature, lattice enthalpy and hydration enthalpy of the individual ions. Amongst fluorides of alkali metals, the lowest solubility of LiF in water is due to
(i) Ionic nature of lithium fluoride
(ii) High lattice enthalpy
(iii) High hydration enthalpy for lithium ion
(iv) Low ionisation enthalpy of lithium atom
The answer is the option (ii) Higher the lattice enthalpy and lower the hydration enthalpy, lower is the solubility of metal halides. In the case of LiF, high lattice enthalpy results in lower solubility.