61. Which of the following is an example of a free radical substitution reaction?
A. Chlorination of methane
B. Nitration of benzene
C. Addition of HCl to propene
D. Reduction of alkenes
Answer: A. Chlorination of methane
Explanation:
In the chlorination of methane, chlorine radicals are generated, which substitute hydrogen atoms in methane to form chloromethane. This reaction proceeds via a free radical mechanism.
62. Which of the following is a nucleophile?
A. H⁺
B. NO₂⁺
C. OH⁻
D. BF₃
Answer: C. OH⁻
Explanation:
A nucleophile is a species that donates a pair of electrons to form a new covalent bond. OH⁻ (hydroxide ion) is a nucleophile because it has a lone pair of electrons.
63. Which of the following compounds undergoes electrophilic substitution easily?
A. Nitrobenzene
B. Benzene
C. Phenol
D. Chlorobenzene
Answer: C. Phenol
Explanation:
Phenol undergoes electrophilic substitution more easily than benzene because the hydroxyl group (-OH) is electron-donating and activates the ring, making it more reactive toward electrophiles.
64. Which of the following is an example of a rearrangement reaction?
A. Wagner-Meerwein rearrangement
B. Hydrolysis of esters
C. Nitration of benzene
D. Addition of HBr to ethene
Answer: A. Wagner-Meerwein rearrangement
Explanation:
The Wagner-Meerwein rearrangement involves the migration of an alkyl group to stabilize a carbocation intermediate during a reaction, making it a rearrangement reaction.
65. Which of the following is the most reactive in an SN2 reaction?
A. Methyl iodide
B. Ethyl iodide
C. Isopropyl iodide
D. Tert-butyl iodide
Answer: A. Methyl iodide
Explanation:
The SN2 reaction is favored by minimal steric hindrance. Methyl iodide, being the least sterically hindered, reacts the fastest in an SN2 mechanism.
66. Which of the following is an example of geometrical isomerism?
A. But-2-ene
B. Butane
C. Ethyne
D. 2-Butanol
Answer: A. But-2-ene
Explanation:
Geometrical isomerism occurs due to restricted rotation around a double bond. In but-2-ene, the position of the substituents around the double bond gives rise to cis and trans isomers.
67. Which of the following undergoes nucleophilic addition reactions?
A. Aldehydes
B. Benzene
C. Ethene
D. Acetylene
Answer: A. Aldehydes
Explanation:
Aldehydes undergo nucleophilic addition reactions because the carbonyl carbon is electrophilic and can be attacked by nucleophiles.
68. Which of the following compounds shows optical isomerism?
A. 2-Chloropropane
B. 2-Bromobutane
C. 2-Butene
D. Cyclohexane
Answer: B. 2-Bromobutane
Explanation:
Optical isomerism occurs when a molecule has a chiral center. 2-Bromobutane has a chiral carbon attached to four different groups, making it optically active.
69. Which of the following is the correct order of stability of carbocations?
A. Methyl < Ethyl < Isopropyl < Tert-butyl
B. Tert-butyl < Isopropyl < Ethyl < Methyl
C. Methyl < Tert-butyl < Ethyl < Isopropyl
D. Isopropyl < Methyl < Ethyl < Tert-butyl
Answer: A. Methyl < Ethyl < Isopropyl < Tert-butyl
Explanation:
Carbocation stability increases with the number of alkyl groups attached to the positively charged carbon. Tertiary (tert-butyl) carbocations are more stable than secondary (isopropyl), primary (ethyl), and methyl carbocations.
70. Which of the following reactions is an example of Markovnikov’s rule?
A. Addition of HCl to propene
B. Addition of HBr to propene in the presence of peroxide
C. Free radical halogenation
D. Oxidation of alkenes
Answer: A. Addition of HCl to propene
Explanation:
Markovnikov’s rule states that in the addition of HX to an unsymmetrical alkene, the hydrogen atom bonds to the carbon with more hydrogen atoms (the less substituted carbon), and the halide bonds to the more substituted carbon.
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