Question

In which of the following processes is energy liberated?

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

Answer 1

The correct option is C $Cl+e^{-}\to C{l}^{-}$

Generally, to determine whether energy is released or absorbed when an electron is added to a neutral gaseous atom, you need to look at the stability of the species.

If we add an electron to Cl atom, energy will be released because $C{l}^{-}$ is more stable than Cl atom.
If we add an electron to N atom, energy will be absorbed because N is more stable than $N^{-}$

In the case of anions, energy is always absorbed when an electron is added.

So, if an electron is added to $O^{-}$ ion a lot of energy is needed to make it $O^{2-}$