The formation of oxide ion 0^{2-} (g) from oxygen atom requires first an exothermic and then an endothermic step as shown below O(g)+e−→O−(g);△H⊝=−141kjmol−1O−(g)+e−⇒O2(g);△H⊝=+780kjmol−1 Thus, process of formation of O2− in gas phase is unfavourable even through O2− is isoelectronic with neon. It is due to the fact that (a) Oxygen si more electronegative (b) addition of electron in oxygen results in larger size of the ion (c) electron repulsiion outweighs the stability gained by achieving noble gas configuration (d) O− ion has comparativly smaller size than oxygen atom

The formation of oxide ion 0^{2-} (g) from oxygen atom requires first

1.	The formation of oxide ion 0^{2-} (g) from oxygen atom requires first an exothermic and then an endothermic step as shown below O(g)+e−→O−(g);△H⊝=−141kjmol−1O−(g)+e−⇒O2(g);△H⊝=+780kjmol−1 Thus, process of formation of O2− in gas phase is unfavourable even through O2− is isoelectronic with neon. It is due to the fact that (a) Oxygen si more electronegative (b) addition of electron in oxygen results in larger size of the ion (c) electron repulsiion outweighs the stability gained by achieving noble gas configuration (d) O− ion has comparativly smaller size than oxygen atom
Answer» The formation of oxide ion 0^{2-} (g) from oxygen atom requires first an exothermic and then an endothermic step as shown below $O (g) + e^{-} \to O^{-} (g); △ H^{⊝} = - 141 k j m o l^{- 1} O^{-} (g) + e^{-} \Rightarrow O^{2} (g); △ H^{⊝} = + 780 k j m o l^{- 1}$ Thus, process of formation of $O^{2 -}$ in gas phase is unfavourable even through $O^{2 -}$ is isoelectronic with neon. It is due to the fact that (a) Oxygen si more electronegative (b) addition of electron in oxygen results in larger size of the ion (c) electron repulsiion outweighs the stability gained by achieving noble gas configuration (d) $O^{-}$ ion has comparativly smaller size than oxygen atom