Q.(a) Which of the following is not applicable to Nylon 6, 6 ?

Nylon 6,6 is a synthetic, condensation-polymerised fibre, not an addition polymer; thermoplastics can be repeatedly softened and remoulded while thermosetting plastics harden permanently on first moulding.

1. Which does not apply to Nylon 6,6 Nylon 6,6 is manufactured by the condensation (step-growth) polymerisation of hexamethylenediamine and adipic acid, with the elimination of water molecules at each linkage (forming amide/peptide bonds), and it is spun into fibres for textile use. So it is: a synthetic polymer (i) - yes; a fibre (ii) - yes; a condensation polymer (iv) - yes. It is not an addition polymer (iii) - addition polymers are formed by simple addition of monomer units (usually containing a C=C double bond) without loss of any small molecule, which is not how nylon 6,6 forms.
2. Thermoplastics vs thermosetting plastics

• Thermoplastics: linear or slightly branched long-chain polymer molecules held together only by weak intermolecular forces (van der Waals/H-bonds), with little or no cross-linking. On heating they soften and can be moulded into a new shape, and on cooling they harden again; this softening-hardening cycle can be repeated many times, so they can be recycled/remoulded. Example: polythene (also PVC, polystyrene). …