Solubility of groups `1` and `2` fluorides increases down the group'. Which of the following is correct explanation for the above given statement ?

Options

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

Explanation

To solve the question regarding the solubility of Group 1 and Group 2 fluorides, we need to analyze the factors affecting solubility, specifically hydration enthalpy and lattice enthalpy.

### Step-by-Step Solution:

1. **Understanding Solubility**:
- The solubility of ionic compounds in water depends on the balance between hydration enthalpy (the energy released when ions are surrounded by water molecules) and lattice enthalpy (the energy required to separate the ions in the solid lattice).
- A compound is soluble if the hydration enthalpy is greater than the lattice enthalpy.

2. **Trends in Group 1 and Group 2 Fluorides**:
- As we move down Group 1 (Li, Na, K, Rb, Cs) and Group 2 (Be, Mg, Ca, Sr, Ba) in the periodic table, the size of the cations increases.
- Larger cations lead to a decrease in hydration enthalpy because the larger size results in a weaker attraction between the cation and water molecules.

3. **Lattice Enthalpy**:
- Similarly, as the size of the cations increases, the lattice enthalpy also decreases. This is because the distance between the ions in the lattice increases, leading to weaker ionic bonds.

4. **Comparing Changes**:
- The decrease in lattice enthalpy is more significant than the decrease in hydration enthalpy as we move down the groups. This means that while both energies decrease, the solubility increases because the lattice enthalpy decreases faster than the hydration enthalpy.

5. **Conclusion**:
- Therefore, the correct explanation for the increase in solubility of Group 1 and Group 2 fluorides down the group is that both hydration and lattice enthalpy decrease, but the decrease in lattice enthalpy is more rapid. This leads to an overall increase in solubility.

### Final Answer:
The correct explanation is: **Both the hydration and lattice enthalpy decrease down the group from top to bottom, but the decrease in lattice energy is rapid.**

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