What is the repeat unit of poly(ethene) represented by?

The repeat unit of poly(ethene) is represented by the structure CH2=CH2, which denotes ethene (orethylene), the monomer from which poly(ethene) is synthesized. During the polymerization process, the double bond between the carbon atoms in ethene opens up, allowing the carbon atoms to link together and form long chains. Each repeat unit of the polymer corresponds to the original ethene molecule, which when repeated forms the polymer structure.

The reason the other options do not represent the repeat unit of poly(ethene) is that they either contain different functional groups that are not part of the structural formula of poly(ethene) or represent different chemical species entirely. The repeat unit must reflect the structure of the monomer used to create the polymer, which is why CH2=CH2 is the correct answer. The polymer itself is made up of long chains of –CH2– units linked together, hence this is the essence of poly(ethene) as derived from ethene.