"Solubility of alkali metal fluorides increases down the group " Select correct explanation for given statement`:`

Options

A. Hydration energy increases and lattice energy decreases down the group
B. Both energy decrease down the group but decrease in hydration energy is rapid
C. Both energy decrease down the group but decrease in lattice energy is rapid
D. Both energy increase down the group but increase in hydration energy is rapid

Answer

To explain why the solubility of alkali metal fluorides increases down the group, we can break down the reasoning into several steps:

### Step-by-Step Solution:

1. **Understanding Alkali Metal Fluorides**:
- Alkali metal fluorides consist of alkali metal ions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and fluoride ions (F⁻). The fluoride ion remains constant in size, while the size of the alkali metal ions increases down the group.

2. **Size of Metal Ions**:
- As we move down the group from lithium to cesium, the size of the alkali metal ions increases. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons.

3. **Lattice Energy**:
- Lattice energy is the energy required to separate one mole of a solid ionic compound into its gaseous ions. As the size of the metal ion increases, the lattice energy decreases because the electrostatic attraction between the larger metal ion and the smaller fluoride ion becomes weaker.

4. **Hydration Energy**:
- Hydration energy is the energy released when ions are surrounded by water molecules. As the size of the metal ions increases, the charge density (charge per unit volume) decreases, leading to a decrease in hydration energy. However, this decrease is less significant compared to the decrease in lattice energy.

5. **Comparison of Lattice and Hydration Energies**:
- While both lattice energy and hydration energy decrease down the group, the decrease in lattice energy is more pronounced. This means that the solubility of alkali metal fluorides increases because the energy required to break the ionic bonds (lattice energy) decreases more rapidly than the energy released when the ions are hydrated (hydration energy).

6. **Conclusion**:
- Therefore, the overall solubility of alkali metal fluorides increases down the group due to the faster decrease in lattice energy compared to hydration energy.

### Final Answer:
The correct explanation for the statement "Solubility of alkali metal fluorides increases down the group" is that both lattice energy and hydration energy decrease down the group, but the decrease in lattice energy is more rapid.

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