`F` has the highest electronegativity among the group `17` elements (i.e. `ns^(2) np^(2) np^(5)` type), on the Pauling scale, but the `EA` of `F` is less than that of `Cl` because

Options

A. `F` being the first member of the family behaves in an unusual manner.
B. The atomic number of `F` is less than that of `Cl`.
C. `Cl` can accommodate an electron better than `F` by utilsing its vacant `3d` orbital.
D. Small size, high `EN` and an increased electron-electron replusion makes addition of an electron to `F` less favourable.

Answer

To understand why fluorine (F) has a lower electron affinity (EA) than chlorine (Cl) despite having the highest electronegativity among the group 17 elements, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Definition of Electronegativity and Electron Affinity**:
- Electronegativity is the tendency of an atom to attract shared electrons in a chemical bond. Fluorine has the highest electronegativity on the Pauling scale.
- Electron affinity (EA) is the amount of energy released when an electron is added to a neutral atom to form a negative ion.

2. **Comparison of Electron Configurations**:
- Fluorine has the electron configuration of 1s² 2s² 2p⁵, meaning it has 7 electrons in its outer shell and needs one more to complete its octet.
- Chlorine has the electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁵, with 7 electrons in its outer shell as well, but it is in a higher energy level (n=3).

3. **Size and Electron Repulsion**:
- Fluorine is smaller in size compared to chlorine. The small size of fluorine leads to greater electron-electron repulsion when an additional electron is added to its already filled 2p subshell.
- In contrast, chlorine, being larger, has more space in its 3p subshell to accommodate an additional electron, which reduces the electron-electron repulsion.

4. **Energy Considerations**:
- The energy released when adding an electron to fluorine is less favorable due to the high electron-electron repulsion in the small 2p orbital.
- Chlorine can accommodate the additional electron more easily, leading to a higher electron affinity.

5. **Conclusion**:
- Therefore, despite fluorine having the highest electronegativity, its electron affinity is lower than that of chlorine because the small size of fluorine leads to increased electron-electron repulsion, making the addition of an electron less favorable.

### Final Answer:
The reason that fluorine has a lower electron affinity than chlorine, despite having the highest electronegativity, is due to the small size of fluorine leading to increased electron-electron repulsion, which makes the addition of an electron less favorable.