Question

The correct order of electron gain enthalpy is :

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Answer 1

Electron affinity values for group $16$ elements:
$O=141kJ/molS=200kJ/molSe=195kJ/molTe=190kJ/molPo=174kJ/mol$
Correct order of electron gain enthalpy is
$S>Se>Te>O$

Lesser the electronic repulsion faced by an electron to get occupied in the outermost shell higher the amount of energy released.

On moving down the group, the electron gain enthalpy decreases from $S$ to $Po$.
Oxygen has an unexpectedly low value of electron gain enthalpy.
Since oxygen is smaller in size than $S$, so incoming $e^{-}$ on oxygen faces more electronic repulsion due to more $e^{-}$ density as a result electron affinity decreases.