Which one of the following structures represents the neoprene rubber?

$A$ polymer sample contains $10$ molecules each with molecular mass $5,000$ and $5$ molecules each with molecular mass $50,000$. The number average molecular mass of the polymer sample is

Nylon threads are made of

The polymer used for making contact lenses for eyes is

Match List-$I$ with List-$II$ :
| List-$I$ | List-$II$ |
| :--- | :--- |
| $(a)$ Chloroprene | $(i)$ $CH_2=C(CH_3)-CH=CH_2$ |
| $(b)$ Neoprene | (ii) $CH_2=C(Cl)-CH=CH_2$ |
| $(c)$ Acrylonitrile | (iii) $[-CH_2-C(Cl)=CH-CH_2-]_n$ |
| $(d)$ Isoprene | (iv) $CH_2=CH-CN$ |
Choose the correct answer from the options given below :

Caprolactam is used for the manufacture of