Question

Which of the following processes absorb energy?

• A. $O+e^{-}\to O^{-}$
• B. $F+e^{-}\to F^{-}$
• C. $Li+e^{-}\to L{i}^{-}$
• D. $O^{-}+e^{-}\to O^{2-}$

Answer 1

The correct option is D $O^{-}+e^{-}\to O^{2-}$

When an electron is added to neutral gaseous species to get an anion, energy is released which is called electron affinity. For the processes given in option (a), (b) and (c) energy is released i.e. $1^{st}$ electron affinity.
In option (d), an electron is being added to an anion. The $2^{nd}$ electron affinity involves an absorption of energy as it has to overcome the effect of repulsion.