Question

The process requiring the absorption of energy is:

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

Answer 1

Answer: (B)

Energy is released when first electron is added to neutral atom. But energy is absorbed when electron is added to an ion because the anion already has excess of electron and in order to add one more electron energy needed to be supplied.
[a] $F+e^{-}\to F^{-}$Energy is released
[b] $Cl+e^{-}\to C{l}^{-}$Energy is released
[c] $O+e^{-}\stackrel{-\Delta H}{\to }{O}^{-}\underset{+\Delta E}{\overset{+\text{ electron }}{\to }}{O}^{2-}$
$\therefore$ In overall reaction energy is absorbed.
[d] $H+e^{-}\to H^{-}$energy is released.