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

Options

A. Hydrogen energy increase and lattice energy decrease 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 understand why the solubility of alkali metal fluorides increases down the group, we need to analyze the factors affecting solubility: hydration energy and lattice energy.

### Step-by-Step Solution:

1. **Identify Alkali Metal Fluorides**:
- Alkali metal fluorides are compounds formed by alkali metals (Li, Na, K, Rb, Cs) combined with fluorine (F).

2. **Understand Solubility**:
- Solubility refers to the ability of a substance to dissolve in a solvent. For ionic compounds like alkali metal fluorides, solubility in water is influenced by hydration energy and lattice energy.

3. **Define Hydration Energy**:
- Hydration energy is the energy released when ions are surrounded by water molecules. It is inversely proportional to the size of the cation. As the size of the cation increases, the hydration energy decreases.

4. **Define Lattice Energy**:
- Lattice energy is the energy required to separate one mole of an ionic compound into its gaseous ions. It depends on the distance between the ions; larger ions lead to longer bond lengths, which results in lower lattice energy.

5. **Analyze Trends Down the Group**:
- As we move down the group from Li to Cs:
- The size of the cation increases (Li+ < Na+ < K+ < Rb+ < Cs+).
- Consequently, hydration energy decreases due to the larger size of the cations.
- Simultaneously, the lattice energy also decreases because larger cations lead to increased bond lengths.

6. **Evaluate the Effect on Solubility**:
- The solubility of alkali metal fluorides depends on the balance between hydration energy and lattice energy.
- While both energies decrease down the group, the decrease in lattice energy is more significant than the decrease in hydration energy. This results in an overall increase in solubility.

7. **Conclusion**:
- Therefore, the correct explanation for the statement "solubility of alkali metal fluorides increases down the group" is that both hydration energy and lattice energy decrease, but the decrease in lattice energy is more pronounced, leading to increased solubility.