Which among the following polymers does not show cross-linking?

Which among the following is a cross-linked polymer?

$A$ polymer contains $50$ molecules with molecular mass $5,000$, $100$ molecules with molecular mass $10,000$ and $50$ molecules with molecular mass $15,000$. Calculate the number average molecular mass. (in $,000$)

Which of the following polymers is grouped in the category of elastomers?

Natural rubber is a

Teflon,Styron (Polystyrene),and Neoprene are all ....... .