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 determine why lithium fluoride (LiF) has the lowest solubility in water among the alkali metal fluorides, we need to analyze the concepts of lattice enthalpy and hydration enthalpy.

### Step-by-Step Solution:

1. **Understanding Lattice Energy**:
- Lattice energy is the energy released when gaseous ions combine to form an ionic solid. It is influenced by the charges of the ions and their sizes. The greater the charge and the smaller the size of the ions, the higher the lattice energy.

2. **Understanding Hydration Energy**:
- Hydration energy is the energy released when ions are surrounded by water molecules and solvated. It depends on the size of the ions; smaller ions typically have higher hydration energies because they can interact more effectively with water molecules.

3. **Comparing Lattice and Hydration Energies**:
- For a salt to be soluble in water, the hydration energy must be greater than the lattice energy. If the lattice energy is too high, it can outweigh the hydration energy, leading to low solubility.

4. **Analyzing LiF**:
- Lithium (Li) is the smallest alkali metal cation, and fluoride (F) is the smallest halide anion. This results in a very high lattice energy for LiF due to the small size and high charge density of both ions.

5. **Conclusion**:
- The high lattice energy of LiF makes it less soluble in water compared to other alkali metal fluorides. The lattice energy of LiF is greater than its hydration energy, which is why it has the lowest solubility among the alkali metal fluorides.

### Final Answer:
The lowest solubility of LiF in water is due to its high lattice energy, which exceeds its hydration energy.

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