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.