Which of the following processes is exothermic?

• A
  $S_{(g)} + 2e^- \rightarrow S^{2-}_{(g)}$
• B
  $N_{(g)} + e^- \rightarrow N^-_{(g)}$
• C
  $Al^{2+}_{(g)} \rightarrow Al^{3+}_{(g)} + e^-$
• D
  $Na^+_{(g)} + Cl^-_{(g)} \rightarrow NaCl_{(s)}$