The substances that on heating undergo polymerization reaction are

i) Methane         ii) Hydrogen       iii) Styrene        iv) Ethylene

 Styrene, Ethylene. Are important materials in the plastic industry. These undergo polymerization and form, polymers.

Ethylene monomer upon hearing undergoes polymerization and forms polythene.

Similarly, styrene molecule upon heating at a suitable temperature forms polystyrene.