Energy is released in the process of

(A) Na_(g) →Na⁺_(g) + e ; this represents Ionization energy(required energy by the removal of electron).

(B) O^–_(g) + e → O^–2_(g)  : this represents 2^nd electron affinity(energy is required to avoid repulsions between added electron and existing electron)

(C) N^–2_(g) + e → N^–3_(g) ; this represents 3^rd electron affinity(energy is required to avoid repulsions between added electron and existing electron)

(D) O_(g) + e →O^–_(g) ; this represents electron affinity(released energy on addition of electron).