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

Options

A. ionic nature of lithium fluoride
B. high lattice enthalpy
C. high hydration enthalpy for lithium ion
D. low ionisation enthalpy of lithium atom

Explanation

To answer the question regarding the low solubility of lithium fluoride (LiF) in water, we need to analyze the factors affecting solubility, specifically the lattice enthalpy and hydration enthalpy of the ions involved.

### Step-by-Step Solution:

1. **Understanding Lattice Enthalpy**:
- Lattice enthalpy is the energy required to separate one mole of a solid ionic compound into its gaseous ions. For LiF, this means breaking it into Li⁺ and F⁻ ions.
- The lattice enthalpy of LiF is very high due to the small size and high charge density of both Li⁺ and F⁻ ions.

2. **Understanding Hydration Enthalpy**:
- Hydration enthalpy is the energy released when gaseous ions are surrounded by water molecules and solvate. This process generally favors solubility.
- While the hydration enthalpy for Li⁺ is relatively high, the hydration enthalpy of F⁻ is not sufficient to overcome the high lattice enthalpy of LiF.

3. **Comparing Lattice and Hydration Enthalpy**:
- For a compound to be soluble, the hydration enthalpy must be greater than the lattice enthalpy. In the case of LiF, the lattice enthalpy is so high that it cannot be compensated by the hydration enthalpy.
- Therefore, the energy required to break the ionic bonds in LiF is greater than the energy released during hydration.

4. **Conclusion**:
- The low solubility of LiF in water is primarily due to its high lattice enthalpy, which is not sufficiently compensated by the hydration enthalpy of the ions.

### Final Answer:
The lowest solubility of LiF in water is due to its high lattice enthalpy, which is greater than the hydration enthalpy of the ions.

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