Which one has greater electron affinity and why ? Cl or F [2]

Fluorine ($\mathrm{F}$) has less electron affinity than chlorine ($\mathrm{Cl}$) despite being more electronegative. This is due to:

1. Smaller atomic size of F: Its compact 2p orbital experiences strong electron–electron repulsion when an extra electron is added, raising the energy of the added electron.
2. Higher electron density: The incoming electron in $\mathrm{F}$ faces significant repulsion from the existing 2s²2p⁵ electrons, making the process less exothermic.
3. Data: The electron affinity of $\mathrm{F}$ is −328 kJ mol⁻¹, while that of $\mathrm{Cl}$ is −349 kJ mol⁻¹ (more negative = greater affinity).

Thus, $\mathrm{Cl}$ has a greater electron affinity than $\mathrm{F}$.