Addition polymerization requires unsaturated monomers like alkenes

Steps:

• Identify monomers suitable for addition polymerization: those with C=C or C≡C bonds that can open for chain growth.
• Examine each formula for unsaturation or reactive groups enabling addition.
• Check if the compound forms polymers via addition (no by-product loss) rather than condensation.
• Select the option with at least one valid compound.

Why A is correct:

• C₂H₄ is ethene, with a C=C double bond that undergoes addition polymerization to form polyethylene, per the mechanism where the pi bond breaks to link monomers.

Why the others are wrong:

• B: CH₂Cl is chloromethane, a saturated alkane derivative lacking double/triple bonds for addition.
• C: CH₂O is formaldehyde, which polymerizes via condensation (forming polyoxymethylene with water loss), not addition.
• D: Not enough information (blank option).

Final answer: A