150. Which claim about polymer growth is false?
[JEE Main Online 15 Apr Evening Chemistry — 2018]
(A) Step-growth polymerisation generally uses bifunctional monomers
(B) Nylon-6 can form by a step-growth pathway
(C) Chain-growth methods can make homopolymers and copolymers
(D) Chain-growth reactions can form only homopolymers
Answer: (D) Chain-growth reactions can form only homopolymers
Explanation: Chain-growth reactions can combine one monomer type into a homopolymer or multiple monomer types into a copolymer, as in styrene-butadiene rubber. Therefore claiming that chain-growth reactions produce homopolymers only is false. Step-growth chemistry commonly uses bifunctional monomers that join progressively.
149. Which alkene produces acetone on ozonolysis?
[RPSC Senior Teacher Science — 01 Jul 2017]
(A) But-2-ene
(B) But-1-ene
(C) 2,3-dimethylbut-2-ene
(D) Propene
Answer: (C) 2,3-dimethylbut-2-ene
Explanation: Ozonolysis cleaves the carbon-carbon double bond and converts its two ends into carbonyl-containing fragments. In 2,3-dimethylbut-2-ene, each double-bond carbon carries two methyl groups, so cleavage gives acetone. The alternative alkenes yield different aldehyde or ketone products.
148. With reference to algae biofuels:
1. Production is possible only in seas.
2. High technical expertise is needed.
3. Large installations can raise ecological concerns.
Which statements are correct?
[UPSC CSE Prelims — 2017]
(A) 1 and 2 only
(B) 2 and 3 only
(C) 3 only
(D) 1, 2 and 3
Answer: (B) 2 and 3 only
Explanation: Algae can be cultivated in freshwater, saline environments or engineered land-based systems; production is not restricted to seas. However, converting algae into commercially viable fuel requires technological expertise, and large facilities can present resource-use and environmental challenges. Thus statements 2 and 3 are correct.
147. Regarding the Climate and Clean Air Coalition:
1. It is a G20-only initiative.
2. It targets methane, black carbon and hydrofluorocarbons.
Which is correct?
[UPSC CSE Prelims — 2017]
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Answer: (B) 2 only
Explanation: The coalition was launched through cooperation among multiple countries and international partners rather than as a G20-only institution. It seeks to reduce short-lived climate pollutants such as methane, black carbon and hydrofluorocarbons, thereby improving air quality and mitigating near-term warming.
146. What is the principal action of the chloroxylenol–terpineol mixture?
[NEET Chemistry — 2017]
(A) Antiseptic
(B) Antipyretic
(C) Antibiotic
(D) Analgesic
Answer: (A) Antiseptic
Explanation: Chloroxylenol is a phenolic antibacterial compound, and terpineol is a terpene alcohol used in some disinfectant mixtures. Together they provide antiseptic action that limits microbial growth on appropriate surfaces or tissues. They are not chiefly fever reducers, systemic antibiotics or pain medicines.
145. Formation of which listed polymer involves hydrolysis of a cyclic monomer?
[JEE Main Offline Chemistry — 2017]
(A) Bakelite
(B) Nylon-6,6
(C) Terylene
(D) Nylon-6
Answer: (D) Nylon-6
Explanation: Nylon-6 can be produced by ring-opening chemistry of caprolactam, including pathways involving water-mediated hydrolysis to aminocaproic acid followed by polymer formation. Nylon-6,6 and Terylene generally arise from condensation of two complementary bifunctional monomers. The cyclic monomer distinguishes nylon-6.
144. Which statements about vinegar are correct?
A. Sugarcane juice can be fermented to make vinegar.
B. Vinegar contains acetic acid.
C. Its characteristic acid is benzoic acid.
D. It preserves food.
[RPSC RAS Prelims — 2016]
(A) A, C and D
(B) A, B and D
(C) A, B and C
(D) B, C and D
Answer: (B) A, B and D
Explanation: Fermentation of sugar-rich feedstock can yield ethanol, which bacteria convert into acetic acid. Vinegar therefore contains ethanoic rather than benzoic acid as its characteristic acid. Its acidic environment inhibits many spoilage microbes, making statements A, B and D correct.
143. What does the abbreviation PVC mean in the plastics industry?
[WBCS Prelims — 2016]
(A) Phospho vinyl chloride
(B) Polyvinyl carbonate
(C) Polyvinyl chloride
(D) Polyvinyl phosphate
Answer: (C) Polyvinyl chloride
Explanation: PVC refers to polyvinyl chloride, a thermoplastic formed by polymerising vinyl chloride. Because of its durability and ease of processing it is widely used in fittings, pipes and electrical insulation. This is a separate year-specific examination occurrence from similar PVC questions.
142. Which gases are included in the urban Air Quality Index: 1 CO₂, 2 CO, 3 NO₂, 4 SO₂, 5 methane?
[UPSC CSE Prelims — 2016]
(A) 1, 2 and 3 only
(B) 2, 3 and 4 only
(C) 1, 4 and 5 only
(D) All five
Answer: (B) 2, 3 and 4 only
Explanation: India’s National Air Quality Index monitors pollutants including carbon monoxide, nitrogen dioxide and sulphur dioxide. Carbon dioxide and methane are important greenhouse gases but are not among the standard AQI component pollutants. Thus the correct gas numbers are 2, 3 and 4.
141. Which medicine among these is an analgesic?
[NEET Phase 1 Chemistry — 2016]
(A) Streptomycin
(B) Chloromycetin
(C) Novalgin
(D) Penicillin
Answer: (C) Novalgin
Explanation: Novalgin is associated with metamizole, an analgesic and antipyretic compound. Streptomycin, chloromycetin and penicillin are antibiotics used against susceptible bacterial infections. Recognising therapeutic drug classes is one application of organic chemistry and the study of biologically active molecules.
