Polymers

To solve this problem, we need to evaluate each statement about the polymers and determine the correct ones.

1. Analyzing Option A: The polymerization of chloroprene gives natural rubber.
Chloroprene is the monomer used in the production of neoprene, not natural rubber. Natural rubber is obtained from the polymerization of isoprene, not chloroprene. Therefore, this statement is incorrect.

2. Analyzing Option B: Teflon is prepared from tetrafluoroethene by heating it with persulphate catalyst at high pressures.
Teflon is indeed prepared by the polymerization of tetrafluoroethylene (TFE), but the process involves heating it in the presence of a free radical initiator like persulfate, at high temperatures and pressures. This statement is correct.

3. Analyzing Option C: PVC are thermoplastic polymers.
Polyvinyl chloride (PVC) is a thermoplastic polymer, meaning it can be melted and remolded. This statement is correct.

4. Analyzing Option D: Ethene at 350-570 K temperature and 1000-2000 atm pressure in the presence of a peroxide initiator yields high-density polythene.
This statement is correct. High-density polyethylene (HDPE) is produced under high pressure and temperature conditions using a peroxide initiator.

Final Answer: The correct options are B, C.