Which of the following is NOT a type of chemical reaction?

In the context of chemical reactions, the correct answer identifies that absorption is not classified as a type of chemical reaction. Synthesis, decomposition, and combustion are all recognized categories of chemical reactions.

Synthesis reactions involve two or more substances combining to form a new compound, which can be represented generically as A + B → AB. Decomposition reactions are the opposite; they involve a single compound breaking down into two or more simpler substances, exemplified by the reaction AB → A + B. Combustion reactions, on the other hand, typically involve a substance reacting with oxygen to produce heat and light, commonly resulting in carbon dioxide and water when hydrocarbons are burned.

Absorption, however, refers to the process by which one substance takes up or incorporates another. This process does not fit the criteria of a chemical reaction, as it does not involve the breaking or forming of chemical bonds or the rearrangement of atoms to create new substances.

Understanding the distinctions among these different processes helps clarify the classifications within chemistry and emphasizes how reactions operate at the molecular level.