Question

The formation of the oxide ion $O^{2-}\left(g\right)$ requires first an exothermic and then, an endothermic step as shown below,
$O\left(g\right)+e⟶O^{-}\left(g\right)$; $\Delta H=-142kJ/mol$.
$O^{-}\left(g\right)+e⟶O^{2-}\left(g\right)$; $\Delta H=844kJ/mol$.
This is because:

• A. $O^{-}$ ion has comparatively larger size than oxygen atom
• B. oxygen has high electron affinity
• C. $O^{-}$ ion will resist the addition of another electron
• D. oxygen is more electronegative

Answer 1

The correct option is C $O^{-}$ ion will resist the addition of another electron

Option (C) is correct. This is because $O^{-}$ ion will resist the addition of another electron. Anion($O^{-}$) already has a negative electron cloud on itself, and thus, will resist the further addition of a second electron. Hence, energy has to be supplied to overcome the repulsion. Thus, the second step is an endothermic reaction.