Question

Electron affinity is positive, when:

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

Answer 1

Answer: (B)

Electron affinity is the energy change, when an electron is added. When ${\text{O}}^{-}$ changes into ${\text{O}}^{2-},$ the electron affinity is positive i.e., change is endothermic. The reason is that ${\text{O}}^{-}$ repels the incoming electron due to similar charge, hence it needs energy to accept the electron. Hence electron affinity is positive.