Which is classified as thermosetting polymer?

(1) Terylene is a fiber. it is not a thermosetting plastic because on heating they melt and don't show the plastic property.

(2) Neoprene rubber is a thermoplastic elastomers.

(3) Polysiloxanes cannot be reused. It is obtained by the irreversible hardening of the siloxane and it is a thermosetting polymer.

(4) Polystyrene is a thermoplastic that is available in a wide range of formulations.

So, the option $3$ is correct.