Which term describes a reaction in which two or more substances combine to form a single product?

• A. Synthesis
• B. Decomposition
• C. Single replacement
• D. Combustion

Answer: (A)

Synthesis describes a reaction where two or more substances come together to form one product. In synthesis, multiple reactants combine to make a single compound, like hydrogen gas reacting with oxygen to form water, or sodium and chlorine forming sodium chloride. The other processes involve different patterns: a decomposition reaction breaks a single compound into simpler substances; a single replacement reaction swaps one element into a compound to produce new substances; combustion is a rapid oxidation that yields oxides of the elements involved (often carbon dioxide and water).