Which has the more exothermic electron affinity, the oxygen atom or O-? Explain why.?

O(g) + e⁻ → O⁻(g) …… ΔH = electron affinity of O atom
O⁻(g) + e⁻ → O²⁻(g) …… ΔH = electron affinity of O⁻ ion

The O atom has more exothermic electron affinity. This is because the negatively-charged O⁻ ion exerts a higher repulsive force to the negatively-charged incoming electrons causing an endothermic effect.