If a plastic is hard,which substance is added to it to introduce the property of softness?

Natural rubber has

The polymer Buna-$S$ is made of .....

Given below are two statements:
Statement $I:$ Ethene at $333$ to $343 \ K$ and $6-7 \ atm$ pressure in the presence of $AlEt_3$ and $TiCl_4$ undergoes addition polymerization to give $LDP$.
Statement $II:$ Caprolactam at $533-543 \ K$ in $H_2O$ through step growth polymerizes to give Nylon-$6$.
In the light of the above Statements,choose the correct answer from the options given below:

The structure shown is a repeating unit for:

The mass average molecular mass and number average molecular mass of a polymer are respectively $40,000$ and $30,000$. The polydispersity index of the polymer will be: