Identify the element having positive electron gain enthalpy.

Among the options, the element with the highest electron gain enthalpy is

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:
$O_{(g)} + e^{-} \longrightarrow O^{-}_{(g)} ; \Delta H^{\ominus} = -141 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^{-} \longrightarrow O^{2-}_{(g)} ; \Delta H^{\ominus} = +760 \ kJ \ mol^{-1}$

For the reaction $Cl_{(g)} + e^- \to Cl^-_{(g)}$,the value of $\Delta H$ is ...........

The correct order of increasing electron affinity of the following elements is

The process requiring the absorption of energy is