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

The formation of the $O^{2-}$ ion is first exothermic and then endothermic,as shown by the following reaction steps:
$O_{(g)} + e^- \to O^-_{(g)}; \Delta H^o = -142 \ kJ \ mol^{-1}$
$O^-_{(g)} + e^- \to O^{2-}_{(g)}; \Delta H^o = 844 \ kJ \ mol^{-1}$
This is due to:

The order of electron affinity for $F, Cl, Br,$ and $I$ is .....

Electron affinity is the

The set containing the elements with positive electron gain enthalpies is

Identify the set of elements in which they are arranged in the increasing order of electron gain enthalpies.