Which of the following transitions involves the maximum amount of energy?

• A
  $M^{-}_{(g)} \to M_{(g)}$
• B
  $M_{(g)} \to M^{+}_{(g)}$
• C
  $M^{+}_{(g)} \to M^{2+}_{(g)}$
• D
  $M^{2+}_{(g)} \to M^{3+}_{(g)}$