The formation of the oxide ion, ${\text{O}}^{2-}(g)$, from oxygen atom requires first an exothermic and then an endothermic step as shown below:$\text{O}(g)+e^{-}⟶{\text{O}}^{-}(g);{\Delta }_f{H}^{\ominus }=-141{\text{kJ mol}}^{-1}$${\text{O}}^{-}(g)+e^{-}⟶{\text{O}}^{2-}(g);{\Delta }_f{H}^{\ominus }=+780{\text{kJ mol}}^{-1}$ Thus the process of formation of ${\text{O}}^{2-}$ in gas phase is unfavourable though ${\text{O}}^{2-}$ is isoelectronic with neon. It is due to the fact that:

1. A
   Oxygen is more electronegative.
2. B
   Addition of electron in oxygen results in larger size of the ion.
3. C
   Electron repulsion outweighs the stability gained by achieving noble gas configuration.
4. D
   ${\text{O}}^{-}$ ion has comparatively smaller size than oxygen atom.