Question

Which one has the positive value of electron affinity: $F$ or $O^{-}$ ?

• A. $O^{-}$
• B. $F$
• C. Both $A$ and $B$
• D. None of the above

Answer 1

The correct option is A $O^{-}$

The addition of second electron to monovalent $O^{-}$ ion to produce $O^{2-}$ ion is difficult due to electrostatic repulsion between same charges (between electron and $O^{-}$ ion). The process becomes endoergic. $EA=+780kJ/mol$
Thus the electron affinity of $O^{-}$ ion is positive.
The electron affinity of F is negative as energy is released when an electron is added to neutral atom.