Assertion (A) :F atom has less electron gain enthalpy than `CI^(Theta)` atom
Reason (R ) : Additional electrons are repelled more effectively by `3p` electron in `CI` atom than by` 2p` electron in F atom

Options

A. If both (A) and (R ) correct and (R ) is the correct explanation for (A)
B. If both (A) and (R ) correct and (R ) is the correct explanation for (A)
C. If (A) is correct but (R ) is incorrect
D. If (A) is incorrect but (R ) is correct

Explanation

To solve the problem, we need to analyze the assertion and reason provided in the question step by step.

### Step 1: Understanding the Assertion
The assertion states that the fluorine (F) atom has less electron gain enthalpy than chlorine (Cl) atom.

- **Electron Gain Enthalpy**: This is the energy change when an electron is added to a neutral atom in the gas phase. Generally, electron gain enthalpy becomes less negative (or more positive) as we move down a group in the periodic table due to increased atomic size and shielding effect.

### Step 2: Analyzing the Assertion
- Fluorine is located above chlorine in Group 17 of the periodic table. According to periodic trends, we would expect fluorine to have a more negative electron gain enthalpy than chlorine because it is smaller and has a higher electronegativity.
- However, fluorine has a very small atomic radius, which leads to significant inter-electronic repulsion when an additional electron is added to its 2p orbital. This repulsion makes the electron gain enthalpy less favorable (less negative) for fluorine compared to chlorine.

### Conclusion for Assertion
Thus, the assertion is **correct**: F has less electron gain enthalpy than Cl.

### Step 3: Understanding the Reason
The reason states that additional electrons are repelled more effectively by the 3p electrons in Cl than by the 2p electrons in F.

### Step 4: Analyzing the Reason
- Chlorine has a larger atomic radius compared to fluorine. The 3p electrons in chlorine are farther from the nucleus than the 2p electrons in fluorine.
- In fluorine, the incoming electron experiences a stronger attraction to the nucleus due to the smaller distance and higher effective nuclear charge, but it also experiences significant repulsion from the already present 2p electrons.
- In chlorine, the incoming electron is farther from the nucleus and experiences less effective nuclear charge and less repulsion from the 3p electrons compared to the repulsion experienced by the incoming electron in fluorine.

### Conclusion for Reason
Thus, the reason is **incorrect**: additional electrons are not repelled more effectively by the 3p electrons in Cl than by the 2p electrons in F.

### Final Conclusion
- Assertion (A) is correct.
- Reason (R) is incorrect.

### Final Answer
The correct option is that Assertion (A) is correct and Reason (R) is incorrect.

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