The diagram shows a section of a polymer - HSC - SSCE Chemistry - Question 6 - 2010 - Paper 1

To identify the systematic name of the monomer, we need to analyze the structure given in the diagram. The diagram shows a repeating unit characteristic of a certain type of polymer, which consists of phenyl (benzene) rings attached to a carbon-carbon backbone.

From the options provided:

• Polybenzene suggests a polymer made purely of benzene units, but this does not accurately reflect the monomer since it doesn't denote a double bond.

• Benzylethene denotes a structure which is not yet a polymeric form and includes a benzene attached to an ethene group, which is not what is shown.

• Ethylbenzene refers to a compound with a two-carbon ethyl group attached to a benzene, which could be a possible candidate but does not represent the repeating unit we've observed.

• Ethenylbenzene accurately describes a vinyl group attached to a phenyl group, which exemplifies the monomer structure depicted in the diagram.

Thus, the correct and systematic name of the monomer in question is Ethenylbenzene (D).