In which of the following reactions does the heat change represent the heat of formation of water?

• A
  $2H_{2(g)} + O_{2(g)} \to 2H_2O_{(l)}; \Delta H = -116 \ kcal$
• B
  $H_{2(g)} + \frac{1}{2}O_{2(g)} \to H_2O_{(l)}; \Delta H = -58 \ kcal$
• C
  $H^{+}_{(aq)} + OH^{-}_{(aq)} \to H_2O_{(l)}; \Delta H = -13.7 \ kcal$
• D
  $C_2H_{2(g)} + 2.5O_{2(g)} \to 2CO_{2(g)} + H_2O_{(l)}; \Delta H = -310 \ kcal$