Which of the following is correct for electron gain enthalpy (with -ve sign) of halogens?

Options

A. Br gt F
B. `Br gt Cl`
C. F gt I
D. F gt Cl

Answer

To solve the question regarding the electron gain enthalpy of halogens, we need to analyze the trends in electron gain enthalpy values for the halogen group (Group 17 elements: fluorine, chlorine, bromine, iodine, and astatine).

### Step-by-Step Solution:

1. **Understanding Electron Gain Enthalpy**:
- Electron gain enthalpy is the energy change that occurs when an electron is added to a neutral atom in the gas phase. A more negative value indicates a greater tendency to gain an electron.

2. **Trends in Halogens**:
- The halogens are arranged in the following order based on their atomic size: Fluorine (F) < Chlorine (Cl) < Bromine (Br) < Iodine (I) < Astatine (At).
- As we move down the group, the atomic size increases, which generally leads to a decrease in the electron gain enthalpy (becomes less negative) due to increased distance from the nucleus and increased electron shielding.

3. **Effective Nuclear Charge**:
- Smaller atoms have a higher effective nuclear charge, making it easier for them to attract additional electrons. Thus, we would expect fluorine to have the highest tendency to gain an electron.

4. **Exception for Fluorine**:
- Although fluorine is the smallest halogen and has a high effective nuclear charge, it experiences significant inter-electronic repulsion due to its small size and high electron density. This makes it less favorable for fluorine to gain an electron compared to chlorine.

5. **Comparing Electron Gain Enthalpy Values**:
- The general trend is:
- Cl > F > Br > I > At
- Chlorine has a more negative electron gain enthalpy than fluorine due to the reasons mentioned above.

6. **Conclusion**:
- The correct order of electron gain enthalpy (with negative signs) for halogens is:
- Cl > F > Br > I > At
- Therefore, statements claiming that bromine has a higher electron gain enthalpy than chlorine or that fluorine has a higher electron gain enthalpy than chlorine are false.

### Final Answer:
The correct order for the electron gain enthalpy of halogens is:
**Cl > F > Br > I > At**.