Chemistry - Thermodynamics - II Question with Solution | TestHub

Reaction $\left(\mathrm{I}\right),\left(\mathrm{II}\right)$ and $\left(\mathrm{IV}\right)$ are of exothermic nature, thus do not involve absorption energy.

The process ${\mathrm{O}}^{-}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}⟶{\mathrm{O}}^{2-}\left(\mathrm{g}\right)$​ involves absorption of energy.

When a neutral atom gains an electron, energy is released. When an anion (having unit negative charge) gains an electron, energy is absorbed. This is due to the repulsion between the additional electron and negatively charged anion.