Answer: Option ii)
Lattice and hydration enthalpies encourage the dissolving of alkali metal halides in water. Fluorides are soluble in this order: LiF, NaF, KF, RbF, CsF. The high lattice energy of LiF makes it insoluble.
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 the lithium atom
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 the lithium atom