The electron gain enthalpy $\Delta_{eg}H$ of $Cl_{(g)}$ is $-349 \ kJ \ mol^{-1}$. If the ground state energy of $Cl_{(g)}$ is $x \ kJ \ mol^{-1}$,the ground state energy (in $kJ \ mol^{-1}$) of $Cl^{-}_{(g)}$ is

Which of the following electronic configurations will have the lowest electron affinity?

What is 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,

The process requiring the absorption of energy is

What is the value of electron gain enthalpy of $Na^{+}$ if $IE_{1}$ of $Na$ is $5.1 \ eV$? .......... $eV$