What describes what occurs in an addition polymerization reaction?

Addition polymerization is a process in which small molecules, known as monomers, chemically react to form a larger, long-chain molecule called a polymer. This reaction typically involves unsaturated monomers that contain double bonds. When these monomers come together, the double bonds are broken, allowing the monomers to link into long chains. As a result, the overall reaction leads to the formation of a macromolecule—a polymer.

This process differs significantly from breaking down large molecules into smaller ones, which is known as degradation or depolymerization. In addition polymerization, the small molecules do not create gas as a byproduct; instead, they combine to form a solid or liquid polymer. Additionally, the rearrangement of small atoms to create different compounds does not involve the formation of polymer chains, which is a key feature of addition polymerization.

Overall, the correct answer accurately encapsulates the concept of addition polymerization by emphasizing the joining of small molecules to create larger, more complex structures.