Statement-1: Lithium's reaction with water is less vigorous than that of sodium.
Statement-2: : Lithium has small size and very high 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 statements provided in the question, we will break down the information step by step.

### Step 1: Understanding Statement 1
**Statement 1:** Lithium's reaction with water is less vigorous than that of sodium.

- **Explanation:** When alkali metals react with water, they produce hydrogen gas and a corresponding hydroxide. The reactivity of alkali metals increases as we move down the group in the periodic table. Sodium, being below lithium, has a more vigorous reaction with water compared to lithium.

### Step 2: Understanding Statement 2
**Statement 2:** Lithium has a small size and very high hydration energy.

- **Explanation:** Lithium is the smallest alkali metal, which means it has a higher charge density. This leads to a high hydration energy when lithium ions are formed. Hydration energy is the energy released when ions are surrounded by water molecules. The small size of lithium results in a strong attraction between the lithium ion and water molecules, leading to high hydration energy.

### Step 3: Connecting the Statements
- The small size and high hydration energy of lithium mean that it holds onto its electrons more tightly compared to sodium. This makes it less reactive with water. In contrast, sodium, being larger and having lower hydration energy, can lose its outer electron more easily, resulting in a more vigorous reaction with water.

### Conclusion
- **Final Analysis:** Both statements are correct. Statement 1 is true because lithium reacts less vigorously with water than sodium. Statement 2 correctly explains the reason for this difference in reactivity due to lithium's small size and high hydration energy.

### Answer
- Both statements are correct, and Statement 2 is the reason for Statement 1.