What type of reaction occurs when alkenes are used to form polymers?

The correct option is Addition reaction..

The correct option is Addition reaction.. Addition reaction. is correct because it directly supports the approved learning objective to when these monomers react they join together, usually losing small molecules such as water, so the reactions are called condensation reactions. This belongs to Polymerisation and naturally occurring polymers within Reactions of alkenes and alcohols (chemistry only), so the answer must use the correct organic chemistry context. The other options are incorrect when they confuse the organic family, formula type, reaction condition, product, or property being tested. Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.