Affinity of oxygen

  1. Which one of the following is correct about the first and second electron affinities of oxygen?
    A) first= slightly exothermic, second = very exothermic
    B) first= sighly exothermic: second = very endothermic
    C) first = slightly endothermic; second = very exothermic
    D) first = slightly endothermic; second = very endothermic
    E) first = very exothermic; second = very exothermic

I chose A but the correct answer is B. May I know the explanation?

Oxygen does not possess a full outer shell meaning that if we add an electron to it we will make it more stable, thus it must release energy and will be exothermic. If we add a second electron there is a strong repulsion between the two negative charges, this requires a lot of energy to overcome. As energy is required the reaction is endothermic.
Hope it helps!