Which of the following pairs is NOT correctly matched?

Rayon is a regenerated cellulose fibre, not a modified starch. Cellulose from wood pulp or cotton linters is dissolved, typically by the viscose process, and extruded through spinnerets to form filaments. So D is the mismatch and is the answer.

Check the other three:

• Oxytocin is a peptide hormone, a nonapeptide released by the posterior pituitary. It drives uterine contraction and milk ejection. Correct match.
• Aspartame is a synthetic dipeptide-based sweetener, roughly 200 times sweeter than sucrose. Correct match.
• Neoprene is polychloroprene, a specialty synthetic rubber known for oil and heat resistance, used in gaskets and wetsuits. Correct match.

Core concept: classifying fibres, plastics and polymers by origin, as natural, regenerated or synthetic. Rayon is the standard regenerated fibre. For Mains, it links to the textile and chemical industry and to the environmental debate over viscose processing and its effluents.

Trap: students see a polysaccharide and a fibre name and pick a starch link. Cellulose and starch are different polysaccharides with different glycosidic linkages, and regeneration is not the same as chemically modifying starch.