The process that is $NOT$ endothermic in nature is :-

The correct electron affinity order is $(EA = -\Delta H_{EG})$

To which of the following atoms is the attachment of an electron most difficult?

What is the correct order of electron affinity for the elements of the oxygen group in the periodic table?

The formation of oxide ion $O^{2-}$ from oxygen atom requires an exothermic reaction,followed by an endothermic step as shown below. The process of formation of $O^{2-}$ in gas phase is unfavorable $(\Delta H^{\ominus} = +ve)$,even though it has the stable configuration of the nearest noble gas neon. This is because:
$O_{(g)} + e^{-} \longrightarrow O^{-}_{(g)} ; \Delta H^{\ominus} = -141 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^{-} \longrightarrow O^{2-}_{(g)} ; \Delta H^{\ominus} = +760 \ kJ \ mol^{-1}$

In which of the following processes is the least energy required?