The formation of the oixde ion, `O^(2+)(g)` from oxygen atom requires first an exothermic and then an endothermic step as shown below:
`O(g)+e^(-) rarr O^(-)(g), Delta H^(O)=-141kJ mol^(-)`
`O(g)+e^(-) rarr O^(-)(g), H^(O)=-kJ mol^(-)`
Thus the process of formation of `O^(2-)` in gas phase is neon. It is due to the fact that

Options

A. Oxygen is more electronegative
B. addition of electrons in oxygen result in larger size of the ion
C. Electron repulsion outweighs the stability gained by achieving noble gas configuration
D. `O^(-)` ion has comparatively smaller size than oxygen atom

Answer

C

Explanation

Second electron gain enthalpy is positive (energy absorbed) due to more repulsion experienced by incoming electrons while entering uninegative anion.