Which out of the `N` or `O` has higher electron gain enthalpy?

Options

A. `Cl,F`
B. `O,S`
C. `O,F`
D. `S,Cl`

Answer

A

Explanation

Negative electron gain enthalpy of F is less than Cl. This is due to the fact that when an electron is added to F, the added electron goes to the smaller `n=2` energy level and experiences significant repulsion from the other electrons present in this level. In `Cl` , the electron goes to the larger `n=3` energy level and consequently occupies a larger region of space leading to much less electron`-` electron repulsion.