Arrange the three halogens $Cl$,$Br$,and $I$ in the increasing order of their electron affinity. Which of the following arrangements is correct?

Which of the following has the maximum electron gain enthalpy?

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

Which halogen has the highest value of negative electron gain enthalpy?

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

In comparison with alkali metals,the electron affinity of halogens is