Which of the following pairs is NOT correctly matched ?

Question

UnlockIAS · Accepted Answer

Correct — D, Rayon — Modified starch. This is the mismatch: rayon has nothing to do with starch. Rayon is REGENERATED CELLULOSE. Wood pulp or cotton linters are chemically dissolved — classically by converting alkali cellulose into sodium cellulose xanthate, the 'viscose' solution — and the solution is then forced through a spinneret into an acid bath, where cellulose is precipitated back out as a continuous, lustrous filament. Because it begins as natural cellulose but is chemically processed and re-formed, rayon is called a semi-synthetic or regenerated fibre, and its shine earned it the trade name 'artificial silk'. Starch and cellulose are both polymers of glucose, but they are different polymers with different linkages, and no commercial rayon is made from starch. The other three pairs are all correctly matched.

Why the other options are wrong — (a) Correctly matched, so not the answer. Oxytocin is a nine-amino-acid peptide hormone synthesised in the hypothalamus and released from the posterior pituitary; it causes uterine contraction during labour and triggers milk ejection (the let-down reflex).  (b) Correctly matched, so not the answer. Aspartame is a man-made dipeptide methyl ester built from aspartic acid and phenylalanine. It is roughly 200 times sweeter than table sugar, so the tiny quantity needed contributes negligible calories — which is exactly why it is sold as a low-calorie artificial sweetener.  (c) Correctly matched, so not the answer. Neoprene is polychloroprene, made by polymerising chloroprene. It is a synthetic rubber (an elastomer) prized for resistance to oil, heat and weathering, and is used in wetsuits, gaskets, hoses and belts.

Concept: This question is really about classifying materials as natural, semi-synthetic or fully synthetic, and matching each to its chemical family. Rayon is semi-synthetic — a natural polymer (cellulose) dissolved and regenerated in fibre form. Neoprene and aspartame are fully synthetic, made by chemical synthesis. Oxytocin is a natural peptide hormone of the body (though it is also manufactured as a drug). Starch and cellulose deserve care: both are glucose polymers of plant origin, but starch has alpha-1,4 links and gives the familiar blue-black colour with iodine, while cellulose has beta-1,4 links, gives no colour with iodine, and is the structural fibre of plants — which is why cellulose, not starch, is the raw material of rayon.

State PCS 2019 Q13 — Science & Technology PYQ with Answer

State PCS 2019 Q13 — Science & Technology PYQ with Answer