The process requiring the absorption of energy is

Which of the following represents the correct order of increasing electron gain enthalpy with negative sign for the elements $O$,$S$,$F$ and $Cl$?

Which of the following is correct for the electron affinity of halogens?

Which of the following atoms should have the highest $1^{st}$ electron affinity?

The formation of the oxide ion,$O^{2-}_{(g)}$ from an oxygen atom requires first an exothermic and then an endothermic step as shown below:
$O_{(g)} + e^- \to O^{-}_{(g)} ; \Delta_f H^o = -141 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^- \to O^{2-}_{(g)} ; \Delta_f H^o = +780 \ kJ \ mol^{-1}$
Thus,the process of formation of $O^{2-}$ in the gas phase is unfavourable even though $O^{2-}$ is isoelectronic with neon. This is due to the fact that,

Which of the following statements regarding electron affinity is correct?