Question

The formation of the oxide ion $O^{2-}\left(g\right)$ requires first an exothermic and then an endothermic step as shown below. $O\left(g\right)+e^{-}=O^{-}\left(g\right);\Delta H^0=-142kJmo{1}^{-1}$
$O(g{)}^{-}+e^{-}=O^{2-}(g);\Delta H^0=844kJmo{1}^{-1}$ This is because:

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

Answer 1

The correct option is C O- ion will tend to resist the addition of another electron

Formation of oxide $O^{-}$ ion is exothermic as octet of oxygen is incomplete but second step is endothermic as already existing negative charge will resist the addition of another charge so we have to give some additional energy to make this happen.