Orlon fibres are made up of:

Orlon is a brand name for the synthetic fiber made from polyacrylonitrile (PAN). Polyacrylonitrile is a vinyl polymer formed by the addition polymerization of acrylonitrile (CH₂=CH-CN) monomers. The repeating unit is -(CH₂-CH(CN))-.

Orlon/Acrylic fibers are widely used in textiles as a wool substitute because they are lightweight, warm, and soft. They are distinct from polyesters (like Dacron/Terylene), polyamides (like Nylon), or natural polymers like cellulose.

Therefore, Orlon fibers are made up of polyacrylonitrile, which is Option 1.