“Orion” (commonly “Orlon”) fibre identification: which statement correctly describes it?

Introduction / Context:
“Orlon” is a trade name historically used for acrylic fibres based on polyacrylonitrile (PAN). The key recognition is the monomer identity and mechanism (addition chain-growth), not condensation.

Given Data / Assumptions:

• Monomer: acrylonitrile (vinyl cyanide).
• PAN can be homopolymer or copolymer with small comonomer amounts, but the classic description is polymerised vinyl cyanide.

Concept / Approach:
Distinguish between chain-growth (vinyl) and condensation (step-growth). Acrylonitrile undergoes addition polymerisation to PAN; thus, the correct choice singles out polymerising vinyl cyanide.

Final Answer:
It is obtained by polymerising vinyl cyanide (acrylonitrile).