UPPSC 2019 Prelims GS Paper-I · Question 13 of 150

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.

• (a)Oxytocin — Hormone — 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)Aspartame — Synthetic sweetner — 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)Neoprene — Specialized rubber — 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.

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.

In a 'NOT correctly matched' pair set, verify each pair independently instead of hunting for the odd one out. Three of these are textbook-safe: hormone, sweetener, synthetic rubber. That isolates rayon, and the only thing you need to remember about rayon is the phrase 'regenerated cellulose / artificial silk'. The word 'starch' is the deliberate trap — it sounds plausible because starch is also a plant carbohydrate.

• Rayon = regenerated cellulose ('artificial silk'), a semi-synthetic fibre; the commonest route is the viscose process
• Starch (alpha-1,4 glucose, gives blue-black with iodine) and cellulose (beta-1,4 glucose, no iodine colour) are different polymers of the same sugar
• Oxytocin = a nine-amino-acid peptide hormone of the posterior pituitary; causes uterine contraction and milk ejection
• Aspartame = aspartic acid + phenylalanine methyl ester, about 200 times sweeter than sucrose; carries a warning for people with phenylketonuria
• Neoprene = polychloroprene, an oil- and weather-resistant synthetic rubber (an elastomer, not a thermoplastic)

• Calling rayon a fully synthetic fibre — it is semi-synthetic, regenerated from natural cellulose
• Treating starch and cellulose as interchangeable because both are glucose polymers
• Confusing neoprene (synthetic polychloroprene) with natural rubber (cis-1,4-polyisoprene from latex)

Both UPPSC and UPSC favour the 'which pair is NOT correctly matched' format for polymers, hormones and food chemicals — and the same names recur, so learning one correct identity per substance covers several years of papers.

• practice — not a real PYQ

  Rayon is best described as:

  • (a)A fully synthetic fibre made from petroleum
  • (b)A semi-synthetic fibre made by regenerating cellulose
  • (c)A natural protein fibre
  • (d)A chemically modified starch

  Answer(b) A semi-synthetic fibre made by regenerating cellulose — wood pulp or cotton linters are dissolved and re-spun into filament, giving rayon its old name 'artificial silk'.

• practice — not a real PYQ

  Which one of the following is a NATURAL polymer?

  • (a)Neoprene
  • (b)Teflon
  • (c)Natural rubber (cis-1,4-polyisoprene)
  • (d)Nylon-6,6

  Answer(c) Natural rubber — obtained as latex from the rubber tree. Neoprene, Teflon and nylon-6,6 are all made by industrial polymerisation.