Which of these equations best illustrates a synthesis reaction?

• A. 2Na + Cl2 -> 2NaCl
• B. NaOH + HCl -> NaCl + H2O
• C. 2H2O2 -> 2H2O + O2
• D. CH4 + 2O2 -> CO2 + 2H2O

Answer: (A)

Synthesis reactions combine two or more substances to form a single new compound. The equation 2Na + Cl2 -> 2NaCl shows this clearly: sodium metal and chlorine gas join to produce a single product, sodium chloride. The other reactions represent different reaction types—neutralization yields salt and water, decomposition breaks a compound into simpler substances, and combustion produces carbon dioxide and water—so they’re not illustrating synthesis.