Question

Electron affinity of $Cl$ is the highest among the halogens, yet $F$ is the strongest oxidising agent. Why?

Answer 1

Electron Affinity of $Cl$ is highest among the halogens. Generally, $EA$ decrease as we move down the group. But $EA$ of $F\left(332.6\right)$ is less than that of $Cl\left(348.5\right)$. Due to very small size of $F$ atom, there are strong electron-electric repulsion is small $2p-$ subshell and thus, the incoming electron does not feel much attraction. Therefore, $F$ has smaller $EA$ than $Cl$ and $EA$ of $Cl$ is highest among the halogens.

Yer, $F$ is strongest oxidizing agent. This is due to following two reasons

1) Bond dissociation energy of $F_2$ is much less than that of $C{l}_2$.

2) Hydration energy of $F_2$ is much higher than, that of $C{l}_2.$

The above two factors compensates for the higher $EA$ of $Cl$. Thus, $F$ is strong oxidizing agent.