The formation of oxide ion O2-(g), from oxygen atom requires first an exothermic and then an endothermic step as shown below.O(g)+e-⟶O-(g);ΔH-=-141 kJ mol-1O-(g)+e-⟶O2( g);ΔH-=+780 kJ mol-1Thus, process of formation of O2- in gas phase is unfavourable even though O2- - is isoelectronic with neon. It is due to the fact that

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oxygen is more electronegative

addition of electron in oxygen results in larger size of the ion

electron repulsion outweighs the stability gained by achieving noble gas configuration

O- ion has comparatively smaller size than O-atom

answer is C.

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Detailed Solution

Although 02- has noble gas configuration isoelectronic with neon but its formation is unfavourable due to the strong electronic repulsion between the negatively charged O- ion and the second electron being added. Hence, the electron repulsion outweighs the stability gained by achieving noble gas configuration

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