Assertion: `F` atom has less negative electron gain enthaply than `Cl` atom.
Reason: Additional electrons are repelled more effectively by 3 p-electrons in `Cl` than by `2` p-electrons in `F` atom.

Options

A. Statement-I is true, Statement-II is true ,Statement -II is the correct explanation for Statement-I
B. Statement-I is true ,Statement -II is true, Statement -II is not the correct explanation for statement -II
C. Statement-I is true. Statement -II is false.
D. Statement-I is false. Statement -II is true.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the fluorine (F) atom has less negative electron gain enthalpy than the chlorine (Cl) atom.
- Electron gain enthalpy is the energy change when an electron is added to a neutral atom in the gas phase. A less negative value indicates that less energy is released when an electron is added.

2. **Understanding the Reason**:
- The reason given is that additional electrons are repelled more effectively by the 3p electrons in chlorine than by the 2p electrons in fluorine.
- This implies that in chlorine, the incoming electron faces less repulsion due to the larger size of the 3p orbital compared to the 2p orbital in fluorine.

3. **Analyzing Electron Configurations**:
- Fluorine has an atomic number of 9, with an electron configuration of 1s² 2s² 2p⁵. When it gains an electron, it becomes F⁻ with a configuration of 1s² 2s² 2p⁶ (stable octet).
- Chlorine has an atomic number of 17, with an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁵. When it gains an electron, it becomes Cl⁻ with a configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ (also stable octet).

4. **Comparing Electron Gain Enthalpy**:
- The electron gain enthalpy for fluorine is less negative than that of chlorine because the added electron in fluorine experiences greater repulsion from the already present electrons in the smaller 2p orbital.
- In contrast, the larger 3p orbital in chlorine allows for less repulsion when an electron is added.

5. **Conclusion**:
- The assertion is true: fluorine has less negative electron gain enthalpy than chlorine.
- The reason is false: the incoming electron is repelled more effectively by the 2p electrons in fluorine, not the 3p electrons in chlorine.

### Final Answer:
- The assertion is true, but the reason is false. Therefore, the correct option is **Option 3**.