Which one (atom/ion) in the following pairs has higher electron gain enthalpy?
(i) ${{O}^{-}}$ , S
(ii)O ,${{S}^{-}}$
(iii)${{O}^{-}}$ , ${{S}^{-}}$
(iv) ${{N}^{-}}$ , P
(i) Due to repulsions between the electrons on ${{O}^{-}}$ and the additional incoming electron, the electron gain enthalpy of ${{O}^{-}}$ is positive while that of S a is negative.
(ii) On similar grounds, the electron gain enthalpy of ${{S}^{-}}$ is positive while that of O is negative.
(iii) Due to small size, repulsions between ${{O}^{-}}$ and the incoming electron is much more than in ${{S}^{-}}$. Therefore, electron gain enthalpy of ${{O}^{-}}$ is more positive than that of ${{S}^{-}}$.
(iv) Due to repulsions between ${{N}^{-}}$ and the incoming electron gain enthalpy of ${{N}^{-}}$ is positive while that P is negative.