Which of the following is a monomer of polythene?

Step 1: Analyze the question We need the monomer (the small repeating unit) that joins together to form polythene (polyethylene).

Step 2: Explain the concept Polythene is made by addition polymerization. In this process, monomers containing a carbon-carbon double bond (unsaturated molecules) open up their double bonds and join end to end to form a long chain.

Step 3: Work through the options

• A. Ethanol (C₂H₅OH): An alcohol with no C=C double bond. It is not used to make polythene.
• B. Vinyl chloride (CH₂=CHCl): It has a double bond, but it is the monomer of PVC (polyvinyl chloride), not polythene.
• C. Ethene (CH₂=CH₂): An unsaturated alkene with a double bond. This is the monomer of polythene.
• D. Ethane (C₂H₆): A saturated alkane with only single bonds. It cannot undergo addition polymerization.

Step 4: The reaction

n CH₂=CH₂ → –(CH₂–CH₂)ₙ–

(ethene, under high pressure and a catalyst, forms polythene, also called polyethylene)

Answer: The monomer of polythene is ethene, which is option C.

Exam tip: The name tells you the monomer: poly + ethene = polyethene (polythene). Likewise, poly + vinyl chloride = PVC, and poly + propene = polypropene. Always look for a double bond when the question asks about addition polymer monomers.