Which one of the following statements is incorrect?

The formation of oxide ion $O^{2-}$ from oxygen atom requires an exothermic reaction,followed by an endothermic step as shown below. The process of formation of $O^{2-}$ in gas phase is unfavorable $(\Delta H^{\ominus} = +ve)$,even though it has the stable configuration of the nearest noble gas neon. This is because:
$O_{(g)} + e^{-} \longrightarrow O^{-}_{(g)} ; \Delta H^{\ominus} = -141 \ kJ \ mol^{-1}$
$O^{-}_{(g)} + e^{-} \longrightarrow O^{2-}_{(g)} ; \Delta H^{\ominus} = +760 \ kJ \ mol^{-1}$

When the first electron gain enthalpy $(\Delta _{eg}H)$ of oxygen is $-141 \ kJ/mol,$ its second electron gain enthalpy is

Identify the correct order of electron gain enthalpy (electron affinity) for the elements $Be, B, C, N$.

The set containing the elements with positive electron gain enthalpies is

Explain the periodicity of electron gain enthalpy of elements in the periodic table.