Assertion :- Solubility of alkali metal hydroxide increases on moving down the group.
Reason :- On moving down the group, hydration energy increases and lattice energy decreases.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

To solve the question, we will analyze the assertion and the reason provided step by step.

### Step 1: Analyze the Assertion
The assertion states that "the solubility of alkali metal hydroxide increases on moving down the group."

- **Understanding Solubility**: Solubility of a substance is influenced by the size of its ions. In the case of alkali metal hydroxides, as we move down the group (from lithium to cesium), the size of the alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) increases.
- **Effect of Size on Solubility**: Larger cations tend to have lower lattice energy due to the increased distance between the ions in the solid state, which makes it easier for water molecules to surround and solvate the ions. Therefore, the assertion is **true**.

### Step 2: Analyze the Reason
The reason states that "on moving down the group, hydration energy increases and lattice energy decreases."

- **Hydration Energy**: Hydration energy is the energy released when ions are surrounded by water molecules. For alkali metals, as the cation size increases, the charge density decreases, which means the hydration energy does not significantly increase; it remains relatively constant.
- **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 cation increases, the lattice energy decreases because the distance between the ions increases, leading to weaker electrostatic attractions.
- **Conclusion on Reason**: The reason provided is partially incorrect because it states that hydration energy increases, which is not true for alkali metal hydroxides. Therefore, the reason is **false**.

### Step 3: Conclusion
Based on the analysis:
- The assertion is **true**.
- The reason is **false**.

Thus, the correct answer is: **Assertion is true but reason is false**.

### Final Answer
**Option C**: Assertion is true but reason is false.

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