Which of the following processes involves absorption of energy?

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

Which one of the following statements is incorrect?

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

Which of the following will have the most negative electron gain enthalpy and which the least negative?
$P, S, Cl, F$
Explain your answer.

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,