Which of the following has the highest electron affinity?

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

The energy evolved is highest for which of the following reactions?

Electronic configurations of four elements $A, B, C$ and $D$ are given below :
$(A)$ $1s^2 2s^2 2p^6$
$(B)$ $1s^2 2s^2 2p^4$
$(C)$ $1s^2 2s^2 2p^6 3s^1$
$(D)$ $1s^2 2s^2 2p^5$
Which of the following is the correct order of increasing tendency to gain electron :

Knowing the electron gain enthalpy values for $O \rightarrow O^{-}$ and $O \rightarrow O^{2-}$ as $-141 \ kJ \ mol^{-1}$ and $702 \ kJ \ mol^{-1}$ respectively,how can you account for the formation of a large number of oxides having $O^{2-}$ species and not $O^{-}$?
(Hint: Consider lattice energy factor in the formation of compounds).

Consider the following conversions:
$(i) \, O_{(g)} + e^- \to O_{(g)}^{-}, \Delta H_1$
$(ii) \, F_{(g)} + e^- \to F_{(g)}^{-}, \Delta H_2$
$(iii) \, Cl_{(g)} + e^- \to Cl_{(g)}^{-}, \Delta H_3$
$(iv) \, O_{(g)}^{-} + e^- \to O_{(g)}^{2-}, \Delta H_4$
Based on the given information,which statement is incorrect?