60 free MCQs on Aldehydes, Ketones and Carboxylic Acids with worked answers and explanations. Aldehydes, ketones, carboxylic acids, and their derivatives (esters, amides, acid chlorides). Key reactions include nucleophilic addition, Aldol condensation, Cannizzaro, and Claisen. Very heavily tested in JEE and NEET.
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Curved arrows show the nucleophile attacking the carbonyl carbon while the C=O pi electrons move onto oxygen, giving a tetrahedral alkoxide intermediate.
Q1.
Which functional group is present in aldehydes?
Answer: A. -CHO
Why: Aldehydes contain the -CHO (formyl) group at the end of the carbon chain.
Q2.
Which functional group is present in ketones?
Answer: B. -C(=O)-
Why: Ketones contain a carbonyl group flanked by two carbon groups.
Q3.
What is the IUPAC name of HCHO?
Answer: B. Methanal
Why: HCHO is the simplest aldehyde; its IUPAC name is methanal.
Q4.
What is the IUPAC name of CH<sub>3</sub>CHO?
Answer: B. Ethanal
Why: CH<sub>3</sub>CHO is ethanal, a two-carbon aldehyde.
Q5.
What is the IUPAC name of CH<sub>3</sub>COCH<sub>3</sub>?
Answer: A. Propanone
Why: CH<sub>3</sub>COCH<sub>3</sub> is propanone, the simplest ketone.
Q6.
Which compound gives a positive Tollens' test?
Answer: B. Aldehyde
Why: Aldehydes reduce Tollens' reagent (ammoniacal silver nitrate) to give a silver mirror.
Q7.
Tollens' reagent is an ammoniacal solution of:
Answer: A. Silver nitrate
Why: Tollens' reagent is ammoniacal silver nitrate, also called silver mirror reagent.
Q8.
Fehling's solution gives a brick-red precipitate with:
Answer: B. Aliphatic aldehydes
Why: Aliphatic aldehydes reduce Fehling's solution to give Cu<sub>2</sub>O (brick-red precipitate).
Q9.
Which compound does NOT give a positive Tollens' test?
Answer: C. Propanone
Why: Propanone is a ketone and does not reduce Tollens' reagent.
Q10.
What is the common name of methanal?
Answer: B. Formaldehyde
Why: Methanal (HCHO) is commonly known as formaldehyde.
Q11.
What is the common name of ethanal?
Answer: B. Acetaldehyde
Why: Ethanal (CH<sub>3</sub>CHO) is commonly known as acetaldehyde.
Q12.
What is the common name of propanone?
Answer: A. Acetone
Why: Propanone (CH<sub>3</sub>COCH<sub>3</sub>) is commonly known as acetone.
Q13.
Nucleophilic addition reactions are characteristic of:
Answer: C. Carbonyl compounds
Why: The electrophilic carbonyl carbon undergoes nucleophilic addition reactions.
Q14.
Schiff's reagent is decolourised by:
Answer: B. Aldehydes
Why: Aldehydes restore the pink/magenta colour of Schiff's reagent.
Q15.
Oxidation of a primary alcohol gives:
Answer: A. Aldehyde
Why: Mild oxidation of primary alcohols gives aldehydes; strong oxidation gives carboxylic acids.
Q16.
Oxidation of a secondary alcohol gives:
Answer: B. Ketone
Why: Secondary alcohols are oxidised to ketones.
Q17.
Formaldehyde is used in the manufacture of:
Answer: B. Bakelite
Why: Formaldehyde reacts with phenol to form Bakelite (a thermosetting resin).
Q18.
Which solution is used to preserve biological specimens?
Answer: B. Formalin
Why: Formalin (40% formaldehyde solution) is used as a biological preservative.
Q19.
Which compound has a carbonyl group at the end of the carbon chain?
Answer: B. Aldehyde
Why: Aldehydes have the carbonyl group at the terminal position of the chain.
Q20.
Which is the simplest ketone?
Answer: C. Acetone
Why: Acetone (propanone) is the simplest ketone with formula CH<sub>3</sub>COCH<sub>3</sub>.
Q21.
Aldol condensation requires an aldehyde or ketone having:
Answer: A. Alpha hydrogen
Why: Alpha hydrogen (adjacent to the carbonyl) is essential for enolate formation in aldol condensation.
Q22.
What is the product of aldol condensation of acetaldehyde followed by dehydration?
Answer: A. Crotonaldehyde
Why: Aldol condensation of two acetaldehyde molecules, followed by dehydration, gives crotonaldehyde (but-2-enal).
Q23.
Cannizzaro reaction is a disproportionation shown by aldehydes with:
Answer: A. No alpha hydrogen
Why: Aldehydes without alpha hydrogen cannot form enolates, so they undergo Cannizzaro disproportionation.
Q24.
Which compound undergoes the Cannizzaro reaction?
Answer: B. Benzaldehyde
Why: Benzaldehyde has no alpha hydrogen and undergoes disproportionation (Cannizzaro reaction).
Q25.
Clemmensen reduction converts a carbonyl group to:
Answer: A. -CH<sub>2</sub>-
Why: Clemmensen reduction (Zn-Hg/HCl) reduces C=O directly to -CH<sub>2</sub>-.
Q26.
Wolf-Kishner reduction uses which reagents?
Answer: B. NH2NH<sub>2</sub> and KOH in ethylene glycol
Why: Wolf-Kishner reduction uses hydrazine and base (KOH) at high temperature to reduce C=O to -CH<sub>2</sub>-.
Q27.
What is the product when acetone reacts with HCN?
Answer: A. Acetone cyanohydrin
Why: HCN adds across the C=O bond of acetone to give 2-hydroxy-2-methylpropanenitrile (acetone cyanohydrin).
Q28.
Grignard reagent reacts with formaldehyde to give (after hydrolysis):
Answer: A. Primary alcohol
Why: Formaldehyde has only one carbon; the Grignard product after hydrolysis is a primary alcohol.
Q29.
Grignard reagent reacts with a non-formaldehyde aldehyde to give (after hydrolysis):
Answer: B. Secondary alcohol
Why: Higher aldehydes give secondary alcohols with Grignard reagents.
Q30.
Grignard reagent reacts with a ketone to give (after hydrolysis):
Answer: C. Tertiary alcohol
Why: Ketones give tertiary alcohols with Grignard reagents.
Q31.
Fehling's test is NOT given by:
Answer: C. Benzaldehyde
Why: Benzaldehyde is an aromatic aldehyde and does not reduce Fehling's solution.
Q32.
Rosenmund reduction converts an acid chloride to:
Answer: A. Aldehyde
Why: Rosenmund reduction (H<sub>2</sub>/Pd-BaSO<sub>4</sub>) reduces acyl chlorides to aldehydes.
Q33.
What is the product of the reaction of acetaldehyde with hydroxylamine?
Answer: A. Oxime
Why: Aldehydes react with hydroxylamine (NH<sub>2</sub>OH) to form oximes (R-CH=N-OH).
Q34.
Which reagent converts toluene to benzaldehyde?
Answer: A. CrO3 in acetic anhydride
Why: The Etard reaction or chromyl chloride (CrO3 in acetic anhydride) oxidises the methyl side chain to -CHO.
Q35.
What type of reaction occurs when acetaldehyde reacts with semicarbazide?
Answer: D. Condensation
Why: Reaction with semicarbazide involves nucleophilic addition followed by loss of water (condensation).
Q36.
Which product is formed in the Perkin reaction of benzaldehyde with acetic anhydride?
Answer: A. Cinnamic acid
Why: Perkin reaction between benzaldehyde and acetic anhydride gives cinnamic acid.
Q37.
Which compound gives a yellow precipitate with 2,4-dinitrophenylhydrazine?
Answer: C. Carbonyl compounds
Why: Carbonyl compounds form coloured 2,4-DNP hydrazones (yellow to orange precipitates).
Q38.
Acetaldehyde on treatment with excess ethanol and dry HCl gives:
Answer: A. Acetal
Why: Two moles of alcohol react with one aldehyde in presence of HCl to form acetal (1,1-diethoxyethane).
Q39.
Which carbonyl compound is least reactive towards nucleophilic addition?
Answer: C. Acetone
Why: Acetone is least reactive due to steric hindrance and +I effect of two methyl groups reducing electrophilicity.
Q40.
What is the major product when benzaldehyde undergoes Cannizzaro reaction with NaOH?
Answer: A. Benzyl alcohol and sodium benzoate
Why: One mole of benzaldehyde is oxidised to sodium benzoate and another is reduced to benzyl alcohol.
Q41.
Which compound gives a positive iodoform test but a negative Tollens' test?
Answer: A. Acetone
Why: Acetone has the CH3CO- group (iodoform positive) but is a ketone (Tollens' negative).
Q42.
The iodoform test is positive for compounds containing the group:
Answer: A. -CH3CO-
Why: The methylcarbonyl group (-CH3CO-) or ethanol/ethanal group reacts with I<sub>2</sub>/NaOH to give iodoform.
Q43.
In the Cannizzaro reaction mechanism, which species undergoes oxidation?
Answer: A. One molecule of aldehyde acts as the hydride donor and gets oxidised
Why: In the Cannizzaro mechanism, one aldehyde molecule transfers a hydride and gets oxidised to carboxylate while the other is reduced to alcohol.
Q44.
Which of these undergoes intramolecular Cannizzaro reaction?
Answer: A. Glyoxal (OHCCHO)
Why: Glyoxal undergoes intramolecular Cannizzaro reaction to give glycolic acid.
Q45.
Why is benzaldehyde less reactive than acetaldehyde towards nucleophilic addition?
Answer: A. Resonance with benzene ring decreases electrophilicity of carbonyl carbon
Why: Conjugation with the phenyl ring delocalises the positive charge on carbonyl carbon, reducing its electrophilicity.
Q46.
What is the product of treating acetaldehyde with dilute NaOH?
Answer: A. 3-Hydroxybutanal (aldol product)
Why: Aldol condensation with dilute base gives 3-hydroxybutanal (the aldol product) without dehydration.
Q47.
Meerwein-Ponndorf-Verley reduction transfers a hydride from:
Answer: A. Aluminium isopropoxide to the carbonyl
Why: MPV reduction uses aluminium isopropoxide; isopropanol acts as the hydride source.
Q48.
Which type of isomerism is shown by CH<sub>3</sub>CHO and HOCH=CH<sub>2</sub>?
Answer: A. Tautomerism
Why: Ethanal and vinyl alcohol are keto-enol tautomers.
Q49.
Which compound gives a positive iodoform test?
Answer: A. Propan-2-ol
Why: Propan-2-ol is oxidised to acetone (CH<sub>3</sub>COCH<sub>3</sub>) under the iodoform conditions, giving a positive test.
Q50.
The order of reactivity towards nucleophilic addition is:
Answer: A. HCHO > CH<sub>3</sub>CHO > CH<sub>3</sub>COCH<sub>3</sub>
Why: Formaldehyde is most reactive (no steric or electronic hindrance); steric and inductive effects decrease reactivity along the series.
Q51.
In the aldol condensation, the alpha carbon acts as:
Answer: A. Nucleophile
Why: The enolate formed at the alpha carbon is nucleophilic and attacks the carbonyl carbon of another molecule.
Q52.
What is the product of the reaction of formaldehyde with excess Grignard reagent (RMgX)?
Answer: A. Primary alcohol
Why: Formaldehyde has only one carbon; addition of RMgX followed by hydrolysis gives a primary alcohol RCH<sub>2</sub>OH.
Q53.
Which compound undergoes self-condensation to give diacetone alcohol?
Answer: A. Acetone
Why: Acetone undergoes self-aldol condensation in the presence of Ba(OH)<sub>2</sub> to give diacetone alcohol.
Q54.
Acrolein (propenal) is formed by dehydration of:
Answer: A. Glycerol
Why: Glycerol undergoes dehydration at high temperature to give acrolein (prop-2-enal).
Q55.
In Beckmann rearrangement, an oxime is converted to:
Answer: A. Amide
Why: Beckmann rearrangement converts a ketone oxime to an amide via migration of the anti group.
Q56.
Acetaldehyde reacts with excess methanol in the presence of dry HCl to form:
Answer: A. 1,1-Dimethoxyethane (acetal)
Why: Two moles of methanol add to acetaldehyde in acidic conditions to form the acetal 1,1-dimethoxyethane.
Q57.
Which statement about Knoevenagel condensation is correct?
Answer: A. An active methylene compound condenses with an aldehyde
Why: Knoevenagel condensation involves condensation between an aldehyde and an active methylene compound (e.g., malonate).
Q58.
What is the alpha carbon in acetone (CH<sub>3</sub>COCH<sub>3</sub>)?
Answer: A. Both methyl carbons
Why: Both methyl carbons are alpha to the carbonyl in acetone, so all six hydrogens are alpha hydrogens.
Q59.
Which compound is formed when two molecules of formaldehyde undergo Cannizzaro reaction?
Answer: A. Methanol and formic acid (sodium formate)
Why: Cannizzaro reaction of formaldehyde gives methanol (reduction) and sodium formate (oxidation).
Q60.
The reaction of acetaldehyde with ammonia gives paraldehyde by:
Answer: A. Trimerisation
Why: Acetaldehyde undergoes trimerisation with traces of acid catalyst to form paraldehyde.