81. Which of the following compounds will give a positive 2,4-DNP test?
a) Ethanol
b) Acetone
c) Acetic acid
d) Benzene
Answer: b) Acetone
Explanation: The 2,4-DNP (2,4-Dinitrophenylhydrazine) test is used to detect carbonyl groups in aldehydes and ketones. Acetone, being a ketone, gives a positive result.
82. The oxidation of propanal using potassium permanganate yields:
a) Propanol
b) Propanoic acid
c) Propanone
d) Ethanol
Answer: b) Propanoic acid
Explanation: Potassium permanganate (KMnO₄) is a strong oxidizing agent that converts aldehydes like propanal into their corresponding carboxylic acids, in this case, propanoic acid.
83. Which of the following will produce benzaldehyde upon oxidation?
a) Toluene
b) Benzyl alcohol
c) Phenol
d) Benzoic acid
Answer: b) Benzyl alcohol
Explanation: Oxidation of benzyl alcohol leads to the formation of benzaldehyde.
84. The reaction of an aldehyde with two equivalents of an alcohol in the presence of an acid catalyst forms:
a) Hemiacetal
b) Acetal
c) Ketal
d) Alcohol
Answer: b) Acetal
Explanation: When an aldehyde reacts with two equivalents of an alcohol under acidic conditions, it forms an acetal, which has two alkoxy groups attached to the same carbon atom.
85. The product of the reaction of acetone with methylamine (CH₃NH₂) is:
a) Alcohol
b) Imine
c) Nitrile
d) Amide
Answer: b) Imine
Explanation: The reaction of a ketone (acetone) with a primary amine (methylamine) results in the formation of an imine (Schiff base), which contains a C=N bond.
86. Which of the following compounds does not undergo the iodoform test?
a) Ethanol
b) Acetaldehyde
c) Acetone
d) Methanol
Answer: d) Methanol
Explanation: Methanol does not undergo the iodoform test because it lacks the necessary CH₃CO- or CH₃CH(OH)- group, which is required for a positive result.
87. In the decarboxylation of carboxylic acids, which of the following is usually eliminated?
a) Hydrogen
b) Oxygen
c) Carbon dioxide
d) Nitrogen
Answer: c) Carbon dioxide
Explanation: Decarboxylation is the loss of carbon dioxide (CO₂) from a carboxylic acid, leaving behind a hydrocarbon or derivative.
88. The product of the reaction of formaldehyde with an excess of Grignard reagent (CH₃MgBr) followed by hydrolysis is:
a) Primary alcohol
b) Secondary alcohol
c) Tertiary alcohol
d) Carboxylic acid
Answer: a) Primary alcohol
Explanation: The reaction of formaldehyde with a Grignard reagent, followed by hydrolysis, gives a primary alcohol. In this case, methanol is produced.
89. Which of the following compounds will give a positive Fehling’s test?
a) Acetone
b) Benzaldehyde
c) Acetaldehyde
d) Benzene
Answer: c) Acetaldehyde
Explanation: Fehling’s test is used to detect reducing sugars and aldehydes. Acetaldehyde gives a positive test, forming a brick-red precipitate of copper(I) oxide.
90. Which of the following reagents will convert an aldehyde into a carboxylic acid?
a) NaBH₄
b) KMnO₄
c) LiAlH₄
d) H₂/Pt
Answer: b) KMnO₄
Explanation: Potassium permanganate (KMnO₄) is a strong oxidizing agent that converts aldehydes into carboxylic acids.
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