Question

Electron affinity is positive, when

• A. $O$ changes into $O^{-}$
• B. $O^{-}$ changes into $O^{2-}$
• C. $O$ changes into $O^{+}$
• D. Electron affinity is always negative

Answer 1

The correct option is B $O^{-}$ changes into $O^{2-}$

The change from $O^{-}$ to $O^{2-}$ is endothermic because $O^{-}$ repels the incoming electron due to its negative charge hence, it needs additional energy to accept the electron. So, the electron affinity is positive.

Hence, option (b) is correct answer.