Q.F2C = CF2 is a monomer of which of the following ?

You already know that plastics are long-chain molecules built from small repeating units called monomers. The three materials you are asking about — Teflon, PVC, and polythene — are all addition polymers, meaning the monomer units simply join together without losing any atoms. What makes them different is the monomer itself, and that difference gives each material a completely different personality.

Let’s start with the simplest: polythene (polyethylene). Its monomer is ethene, $CH_2=CH_2$. When many ethene molecules link up, you get a long chain of $—CH_2—CH_2—$ repeating thousands of times. That chain is flexible, waxy, and cheap. That is why polythene is the plastic of carry bags, milk pouches, and shampoo bottles. It is the workhorse plastic — nothing fancy, just reliable.

Now PVC (polyvinyl chloride). Its monomer is vinyl chloride, $CH_2=CHCl$. Notice the chlorine atom hanging off every second carbon. That chlorine changes everything. It makes the chain polar, so the molecules stick to each other more strongly. PVC is harder and more rigid than polythene. You can also add plasticisers to make it flexible. That is why PVC appears in two very different forms: rigid PVC for pipes and window frames, and flexible PVC for electrical cable insulation and flooring.

Finally Teflon (polytetrafluoroethene). Its monomer is tetrafluoroethene, $CF_2=CF_2$. Every hydrogen in ethene has been replaced by fluorine. The carbon-fluorine bond is one of the strongest in organic chemistry. The fluorine atoms also wrap around the carbon backbone like a protective sheath, making the polymer incredibly inert. Nothing sticks to Teflon — not food, not chemicals, not even water. That is why it is used as a non-stick coating on cookware and as a sealant in chemical plants.