Question

The process that requires an absorption of energy is:

• A. $F\to F^{-}$
• B. $H\to H^{-}$
• C. $Cl\to C{l}^{-}$
• D. $O\to O^{2-}$

Answer 1

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

The amount of energy released when an electron is added to an atom is termed as electron affinity. Here, for all the options apart from option d, the reaction is exothermic. The addition of a second electron to the $O^{-}$ ion requires more energy. The repulsion between the electrons and the ion makes $O\to O^{2-}$ endothermic.

$O\left(g\right)+e^{-}\to O^{-}\left(g\right);E_{A_1}=-142kJ/mol$
$O^{-}\left(g\right)+e^{-}\to O^{2-}\left(g\right);E_{A_2}=+844kJ/mol$
The value of $E_{A_2}$ shows that the process absorbs more energy and hence, endothermic.