A Level Chemistry OCR Practice Exam

The correct answer indicates that addition polymerization of unsaturated alkene molecules results in the formation of very long molecular chains. During this process, the double bonds in the alkene molecules open up and link together, creating a continuous chain of repeating units known as a polymer. In contrast to short or branched chains, addition polymerization typically leads to long, linear chains because the reaction involves the linking of many monomer units in a straightforward manner without branching or backtracking. This is characteristic of addition polymers like polyethylene, which consists of thousands of repeating units of ethylene (the monomer) fused together in a long chain. Additionally, the notion of separate monomer units is inconsistent with the nature of polymerization, where the goal is to form a solid molecular structure through the joining of monomers rather than leaving them as individual entities. Thus, the formation of a very long molecular chain is a defining feature of addition polymers.