31. Which of the following compounds is formed when acetic acid reacts with phosphorus pentachloride (PCl₅)?
a) Acetyl chloride
b) Acetaldehyde
c) Acetone
d) Ethanol
Answer: a) Acetyl chloride
Explanation: Acetic acid reacts with phosphorus pentachloride (PCl₅) to form acetyl chloride and phosphorus oxychloride (POCl₃).
32. The reaction of an aldehyde or ketone with hydroxylamine (NH₂OH) forms:
a) An oxime
b) A hydrazone
c) A cyanohydrin
d) A semicarbazone
Answer: a) An oxime
Explanation: Aldehydes and ketones react with hydroxylamine (NH₂OH) to form oximes.
33. Which of the following is not a reducing agent for the reduction of aldehydes and ketones?
a) NaBH₄
b) H₂/Ni
c) LiAlH₄
d) PCC
Answer: d) PCC
Explanation: PCC (Pyridinium chlorochromate) is an oxidizing agent, not a reducing agent. It is used to oxidize alcohols to aldehydes or ketones.
34. In the Clemmensen reduction, the reagent used is:
a) Zn/Hg in HCl
b) NaBH₄
c) LiAlH₄
d) H₂/Pd
Answer: a) Zn/Hg in HCl
Explanation: Clemmensen reduction involves the reduction of aldehydes or ketones to hydrocarbons using zinc amalgam (Zn/Hg) in hydrochloric acid.
35. Which of the following is the correct order of boiling points for carboxylic acids, aldehydes, and ketones?
a) Carboxylic acids > Aldehydes > Ketones
b) Carboxylic acids > Ketones > Aldehydes
c) Aldehydes > Ketones > Carboxylic acids
d) Ketones > Carboxylic acids > Aldehydes
Answer: b) Carboxylic acids > Ketones > Aldehydes
Explanation: Carboxylic acids have the highest boiling points due to hydrogen bonding. Ketones have higher boiling points than aldehydes because of their greater molecular mass and dipole interactions.
36. Which of the following compounds does not undergo the Cannizzaro reaction?
a) Formaldehyde
b) Benzaldehyde
c) Acetone
d) Trimethylacetaldehyde
Answer: c) Acetone
Explanation: Acetone is a ketone and does not undergo the Cannizzaro reaction, which is specific to aldehydes without alpha-hydrogens.
37. When propanoic acid is treated with phosphorus pentachloride, the product is:
a) Propionyl chloride
b) Propanal
c) Propanone
d) Propanol
Answer: a) Propionyl chloride
Explanation: Propanoic acid reacts with phosphorus pentachloride (PCl₅) to form propionyl chloride and phosphorus oxychloride.
38. Which of the following aldehydes is the least reactive towards nucleophilic addition?
a) Formaldehyde
b) Acetaldehyde
c) Benzaldehyde
d) Propanal
Answer: c) Benzaldehyde
Explanation: Benzaldehyde is less reactive due to the electron-withdrawing effect of the benzene ring, which stabilizes the carbonyl carbon and reduces its electrophilicity.
39. The reaction of an aldehyde with hydrogen cyanide (HCN) forms:
a) An alcohol
b) A cyanohydrin
c) An ester
d) A nitrile
Answer: b) A cyanohydrin
Explanation: Aldehydes react with hydrogen cyanide (HCN) to form cyanohydrins, which contain both a hydroxyl group and a nitrile group.
40. Which of the following compounds undergoes the haloform reaction?
a) Acetone
b) Benzaldehyde
c) Methanal
d) Propanal
Answer: a) Acetone
Explanation: Acetone has a methyl ketone group, which is required for the haloform reaction to occur. This reaction produces iodoform (CHI₃) when iodine is used.
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