Which of the following polymers contains $H$-bonding?

The monomer which is present in both Bakelite and Melamine polymers is

The repeating unit of organosilicon polymers (silicones) is:

$A$ 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

Buna-$S$ can be represented as:

Identify the biodegradable polymer from the following.