What type of reaction occurs when a substance combines with oxygen and releases energy?

A reaction that involves the combination of a substance with oxygen, resulting in the release of energy, is best classified as a combustion reaction. During a combustion reaction, typically a hydrocarbon or other organic material reacts with oxygen, producing carbon dioxide and water as byproducts, along with a significant release of heat and light energy. This is a characteristic feature of combustion processes, which are commonly seen in burning fuels.

In contrast, synthesis reactions involve two or more reactants combining to form a single product, whereas decomposition reactions involve a single reactant breaking down into two or more products. Single replacement reactions involve one element replacing another in a compound. These other types of reactions do not typically involve the direct conversion of a substance into combustion products with the release of energy as seen in combustion reactions. Thus, the defining nature of combustion clearly identifies it as the correct classification for reactions involving the combination with oxygen and the liberation of energy.