A : LiF and Csl both are less soluble in water .
R : LiF is with high lattice energy and Csi is with smaller hydration energy.

Options

A. If both Assertion & Reason are true and the reason is the correct explanantion of the assertion, then mark (1).
B. If both Assertion & Reason are true and the reason is the correct explanantion of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false. Them mark (3).
D. If both Assertion and reason are false statement, then mark (4).

Answer

To analyze the assertion and reason provided in the question, we will break down the concepts of lattice energy, hydration energy, and solubility in water step by step.

### Step 1: Understanding the Compounds
- **Assertion (A)**: Both LiF (Lithium Fluoride) and CsI (Cesium Iodide) are less soluble in water.
- **Reason (R)**: LiF has high lattice energy, and CsI has smaller hydration energy.

### Step 2: Lattice Energy
- **Lattice Energy** is the energy released when gaseous ions combine to form an ionic solid. It is influenced by the size of the ions and their charges.
- **LiF**: Lithium (Li⁺) is a small cation, and Fluoride (F⁻) is a small anion. The small size of both ions leads to a high lattice energy due to strong electrostatic forces between them.
- **CsI**: Cesium (Cs⁺) is a larger cation, and Iodide (I⁻) is a larger anion. The larger size results in a lower lattice energy compared to LiF.

### Step 3: Hydration Energy
- **Hydration Energy** is the energy released when ions are surrounded by water molecules. It depends on the size of the ions; smaller ions typically have higher hydration energy because they can interact more effectively with water.
- **LiF**: Despite having high lattice energy, LiF has low hydration energy because the small size of Li⁺ and F⁻ results in a smaller surface area for water molecules to interact.
- **CsI**: CsI has smaller hydration energy due to the larger size of Cs⁺ and I⁻, which reduces the effectiveness of water molecules in surrounding the ions.

### Step 4: Solubility in Water
- Compounds with high lattice energy and low hydration energy tend to be less soluble in water.
- **LiF**: High lattice energy and low hydration energy contribute to its low solubility.
- **CsI**: Lower lattice energy and low hydration energy also contribute to its low solubility.

### Step 5: Conclusion
- Both assertions are correct:
- **Assertion (A)**: True, both LiF and CsI are less soluble in water.
- **Reason (R)**: True, LiF has high lattice energy, and CsI has smaller hydration energy.

### Final Answer
- Therefore, the correct conclusion is that both the assertion and reason are true, and the reason correctly explains the assertion.