The given chemical equation represents the decomposition of water into hydrogen gas (H2) and oxygen gas (O2), not a synthesis reaction. In a synthesis reaction, multiple reactants combine to form a single product. To determine if a reaction is a synthesis reaction, you need to check if two or more substances are coming together to form a new substance. In this case, a single water molecule is splitting into two separate molecules, so it is a decomposition reaction instead of a synthesis reaction.
