Would you expect the second electron gain enthalpy of $O$ to be positive,more negative,or less negative than the first? Justify your answer.

(A) The first electron gain enthalpy of oxygen is negative because energy is released when an electron is added to a neutral oxygen atom to form an $O^-$ ion.
The second electron gain enthalpy of oxygen is positive. This is because after the addition of the first electron,the oxygen atom becomes a negatively charged $O^-$ ion.
The second electron is added to this negatively charged ion,and the incoming electron experiences strong electrostatic repulsion from the existing negative charge.
Therefore,energy must be supplied to overcome these coulombic repulsions to force the second electron into the anion,making the process endothermic (positive electron gain enthalpy).