[sn1sn2e1e2]

Which process RELEASES the most energy?

(A) Mg2+ (g) + e-    Mg2+(g)
(B) Mg+(g) + e-  Mg(g)
(C) Na2+(g) +e-  Na+(g)
(D) Na+(g) +e-  Na(g)

I chose C because...

Electron Affinity= E(initial) minus E(final) and since Na2+ is highly unstable (so high in energy) and Na+ (low in energy because favorable configuration)= large, position energy release

Can you check if my explanation is correct? ^^^

[Rutherford]

I would choose C, too.

[mjc123]

I agree with C, but saying "Na2+ is higher energy than Na+" is not really an explanation, more a restatement of the question. Why is it higher?
Perhaps it is easier (I find it so) to turn the question round and ask which of the following ionisation processes requires most energy input:
Mg⁺  Mg²⁺ + e
Mg  Mg⁺ + e
Na ⁺  Na²⁺ + e
Na  Na⁺ + e
Ask yourself: which electron is being removed in each case?