Which from following compounds the thermocol is obtained?

Thermocol is the commercial name for expanded polystyrene foam, produced by polymerizing the monomer styrene. Polystyrene forms through addition polymerization of styrene molecules, making styrene the precursor compound.

The correct identification follows from recognizing the polymerization relationship: thermocol $\rightarrow$ polystyrene $\rightarrow$ styrene monomer.