120. Which statement about common antiseptics and disinfectants is incorrect?
[NEET Chemistry — 2013]
(A) Dilute boric acid and hydrogen peroxide are strong antiseptics
(B) Disinfectants may harm living tissues
(C) Phenol can act as an antiseptic at lower concentrations and a disinfectant at higher ones
(D) Chlorine and iodine may be used for disinfection
Answer: (A) Dilute boric acid and hydrogen peroxide are strong antiseptics
Explanation: Dilute boric acid and hydrogen peroxide are typically considered mild rather than strong antiseptics. Many disinfectants are harmful to living tissue, whereas antiseptics are formulated for limited tissue contact. Phenol concentration and the chemistry of halogens affect their antimicrobial applications.
119. Traditional Dettol antiseptic contains which principal pair of organic compounds?
[NEET Karnataka Chemistry — 2013]
(A) Chloroxylenol and bithionol
(B) Chloroxylenol and terpineol
(C) Phenol and iodine
(D) Terpineol and bithionol
Answer: (B) Chloroxylenol and terpineol
Explanation: Traditional Dettol formulations contain chloroxylenol, a substituted phenolic antimicrobial, and terpineol, an organic terpene alcohol. Both names identify aromatic or alcohol functional chemistry relevant to disinfectants. Commercial formulations may change, but this pair is the examination’s prescribed answer.
118. Which type of alcohol reacts most rapidly in the Lucas test, and through what mechanism?
[JEE Main Offline Chemistry — 2013]
(A) Tertiary alcohol via SN1
(B) Secondary alcohol via SN2
(C) Tertiary alcohol via SN2
(D) Secondary alcohol via SN1
Answer: (A) Tertiary alcohol via SN1
Explanation: Tertiary alcohols convert rapidly to alkyl chlorides in concentrated hydrochloric acid and zinc chloride. Their relatively stable tertiary carbocation permits a fast SN1 mechanism. Secondary alcohols react more slowly and primary alcohols usually show little immediate turbidity in the conventional test.
117. TNT (trinitrotoluene) is a/an:
[Chhattisgarh Police Sub-Inspector Prelims — 2012]
(A) Fertilizer
(B) Explosive
(C) Insecticide
(D) Medicine
Answer: (B) Explosive
Explanation: TNT is the common abbreviation of trinitrotoluene, an aromatic nitro compound used as an explosive. It is not categorised as a fertiliser, insecticide or medicine. This basic identification often appears in general science and awareness examinations.
116. Which set of elements was considered primarily responsible for the origin of life on Earth?
[UPSC CSE Prelims — 2012]
(A) Hydrogen, oxygen and sodium
(B) Carbon, hydrogen and nitrogen
(C) Oxygen, calcium and phosphorus
(D) Carbon, hydrogen and potassium
Answer: (B) Carbon, hydrogen and nitrogen
Explanation: Carbon, hydrogen and nitrogen are core elements of biological molecules and prebiotic organic chemistry. Oxygen, phosphorus and sulphur are also vital to modern life. Among the offered combinations, carbon, hydrogen and nitrogen best represent the basic chemical constituents central to the origin-of-life discussion.
115. Which reagent converts 2-hexyne into trans-2-hexene?
[AIEEE Chemistry — 2012]
(A) Hydrogen with platinum
(B) Lithium in liquid ammonia
(C) Hydrogen with palladium-barium sulphate
(D) Lithium aluminium hydride
Answer: (B) Lithium in liquid ammonia
Explanation: Dissolving-metal reduction of an alkyne using lithium in liquid ammonia adds hydrogen in an overall anti fashion, producing a trans-alkene. Lindlar-type poisoned palladium catalysts instead favour cis-alkenes, while ordinary catalytic hydrogenation can reduce the multiple bond further to an alkane.
114. Which statement about polymers is incorrect?
[AIPMT Prelims Chemistry — 2012]
(A) Artificial silk can be made from cellulose
(B) Nylon-6,6 is an elastomer
(C) Natural rubber is based on isoprene units
(D) Both starch and cellulose are glucose polymers
Answer: (B) Nylon-6,6 is an elastomer
Explanation: Nylon-6,6 is a synthetic polyamide fibre, not an elastomer like natural rubber. Artificial silk or rayon is manufactured from processed cellulose, and both starch and cellulose consist of glucose-derived units. Their differing glycosidic linkages lead to markedly different physical properties.
113. Which of these is not a condensation polymer?
[AIPMT Prelims Chemistry — 2012]
(A) Melamine resin
(B) Glyptal
(C) Dacron
(D) Neoprene
Answer: (D) Neoprene
Explanation: Neoprene forms by addition polymerisation of chloroprene, an unsaturated organic monomer. Dacron and Glyptal are polyesters made by condensation reactions, while melamine-formaldehyde resins also arise through condensation chemistry. The polymerisation mechanism therefore separates neoprene from the other listed materials.
112. Chloramphenicol belongs to which drug category?
[AIPMT Mains Chemistry — 2012]
(A) Antifertility medicine
(B) Antihistamine
(C) Antiseptic and disinfectant
(D) Broad-spectrum antibiotic
Answer: (D) Broad-spectrum antibiotic
Explanation: Chloramphenicol is a broad-spectrum antibiotic that inhibits bacterial protein synthesis by acting on ribosomes. It is chemically distinct from antihistamines and antiseptics. Due to potentially serious adverse effects, including bone-marrow toxicity, its use is restricted and monitored in many clinical settings.
111. Which reagent best initiates cationic polymerisation among the choices?
[AIEEE Chemistry — 2012]
(A) LiAlH₄
(B) HNO₃
(C) AlCl₃
(D) Butyllithium
Answer: (C) AlCl₃
Explanation: Aluminium chloride is a Lewis acid that can generate or stabilise electrophilic initiating species for cationic chain polymerisation. Butyllithium is more typically associated with anionic reactions, and lithium aluminium hydride is a reducing agent. The initiating chemistry depends on the monomer and catalyst system.
