Identify the monomers used for the preparation of Buna-$S$.

The polymer $X$ consists of linear molecules and is closely packed. It is prepared in the presence of triethylaluminium and titanium tetrachloride under low pressure. The polymer $X$ is -

The following structure represents a subunit of a hydrocarbon polymer that may be prepared by a radical polymerization method. Identify the monomer that has been polymerized to make this polymer chain.

Among $(I)-(IV)$,the compound that does not undergo polymerisation under radical initiation is:

Which among the following is an example of a cyclic amide?

Which of the following compounds is used for the production of $Nylon-6,6$?