Which of the following is a homopolymer?

PAN

The correct answer is option 2. PAN.

A homopolymer is a type of polymer where all the repeating units (monomers) along the polymer chain are the same. In other words, it consists of only one type of monomer repeating throughout the polymer structure.

Among the options provided:

1. Buna-N: Buna-N is a copolymer composed of two different monomers, butadiene and acrylonitrile. Therefore, it is not a homopolymer because it contains multiple types of monomers.

2. PAN (Polyacrylonitrile): PAN is a homopolymer. It consists of repeating units of acrylonitrile monomers linked together in a chain. Since acrylonitrile is the only type of monomer present, PAN qualifies as a homopolymer.

3. Dacron: Dacron is a polyester synthesized from the condensation polymerization of ethylene glycol and terephthalic acid. It involves two different monomers, so it is not a homopolymer.

4. Bakelite: Bakelite is a thermosetting phenol-formaldehyde resin. It is formed by the condensation polymerization of phenol and formaldehyde monomers. Like Dacron, it contains two different monomers and is therefore not a homopolymer.

In summary, among the options provided, only PAN (Polyacrylonitrile) qualifies as a homopolymer because it consists of repeating units of a single type of monomer, acrylonitrile, throughout its polymer chain.