Which of the following equations represents a synthesis reaction?
A) $"CH"_4"+2O"_2$$rarr$$"CO"_2"+2H"_2"O"$
B) $"AgNO"_3"+NaCl"$$rarr$$"AgCl"+"NaCl"$
C) $"H"_2"O"_2$$rarr$$"H"_2"+O"_2"$
D) $"2Na"+"Cl"_2"$$rarr$$"2NaCl"$
E) $"Mg"+"2HCl"$$rarr$$"MgCl"_2"+H"_2$
Answer: D