JEE (Main) · Chemistry, Class 12
Aldehydes, Ketones and Carboxylic Acids: JEE Main PYQ, 2020–2025
Aldehydes, Ketones and Carboxylic Acids (Chemistry, Class 12) has been asked 138 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.2 questions a paper, 5% of all Chemistry questions. It is the 7th most-asked of 21 Chemistry chapters. The 2025 shifts had 20 from it in all. Last checked 28 October 2026.
Questions per year, all shifts
Year by year.
| Year | Questions |
|---|---|
| 2020 | 9in 14 papers |
| 2021 | 40in 26 papers |
| 2022 | 29in 24 papers |
| 2023 | 15in 12 papers |
| 2024 | 25in 18 papers |
| 2025 | 20in 17 papers |
JEE (Main) is sat in many shifts a year, each with its own paper; the counts add up every shift. 2021–2024 papers had 30 questions a subject, the others 25.
Inside the chapter
Topics asked most.
- Nucleophilic addition70
- Aldol and Cannizzaro27
- Tests to distinguish aldehydes and ketones21
- Acidity of carboxylic acids20
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10 Aldehydes, Ketones and Carboxylic Acids questions to practise.
Our own questions, written in the JEE Main pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Ethanol and ethanoic acid both contain an O–H group, but ethanoic acid is a far stronger acid (pKa about 4.8, against about 16 for ethanol). What is the main reason?
Answer: (A)
Acidity is governed by how stable the conjugate base is after the proton leaves. The carboxylate ion RCOO⁻ has two equivalent C–O bonds and shares the negative charge between two electronegative oxygens, which is strong resonance stabilisation. The ethoxide ion C2H5O⁻ puts the whole negative charge on one oxygen and the electron-donating alkyl group makes that worse. A less stable conjugate base means a weaker acid, so ethanol is far weaker than ethanoic acid.
Q2 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
In the Cannizzaro reaction of benzaldehyde with concentrated NaOH, which species transfers a hydride ion (H⁻) to the carbonyl carbon of a second benzaldehyde molecule?
Answer: (D)
The first step is nucleophilic addition of OH⁻ to the C=O of one benzaldehyde molecule, giving the alkoxide C6H5–CH(OH)–O⁻. In this adduct the negative oxygen pushes electron density toward carbon, and the C–H hydrogen is transferred with its bonding pair as hydride to the carbonyl carbon of a second benzaldehyde. The donor becomes benzoic acid, which is deprotonated to benzoate, and the acceptor becomes the benzyl alkoxide, which takes a proton to give benzyl alcohol. Hydroxide and enolate cannot donate hydride, and benzoate is the oxidised product.
Q3 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Benzaldehyde and acetophenone (1-phenylethanone) are stirred with dilute sodium hydroxide at 293 K. The major product is:
Answer: (D)
Benzaldehyde has no α-hydrogen, so only acetophenone forms the carbanion, which adds to the carbonyl carbon of benzaldehyde. The aldol loses water readily because the double bond formed is conjugated with the carbonyl group and a benzene ring, giving C₆H₅CH=CHCOC₆H₅, 1,3-diphenylprop-2-en-1-one.
Q4 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Which of the following is the most reactive towards nucleophilic addition?
Answer: (D)
Reactivity towards nucleophiles falls as alkyl or aryl groups are added to the carbonyl carbon, which both reduce its positive charge and crowd it. Methanal, with two hydrogen atoms, is the most reactive: HCHO > CH₃CHO > CH₃COCH₃ > C₆H₅COCH₃.
Q5 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Methanal, ethanal, propanone and 2,2,4,4-tetramethylpentan-3-one (di-tert-butyl ketone, (CH3)3C–CO–C(CH3)3) are each treated with HCN under identical conditions. Which sequence correctly gives their order of decreasing reactivity towards this nucleophilic addition?
Answer: (A)
Nucleophilic addition of HCN to C=O converts a planar sp2 carbon into a crowded sp3 carbon. The rate therefore depends on (i) how electrophilic the carbonyl carbon is, since alkyl groups reduce it by +I, and (ii) steric hindrance to the incoming CN⁻. Methanal has two H atoms, so it is least hindered and most electrophilic. Ethanal has one alkyl group, acetone has two, and the di-tert-butyl ketone has two very bulky groups. Both effects point the same way, so the order is HCHO > CH3CHO > CH3COCH3 > (CH3)3C–CO–C(CH3)3.
Q6 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Oxalic acid, HOOC–COOH, has pKa₁ = 1.25 and pKa₂ = 4.27 at 298 K, while ethanoic acid has pKa = 4.76. Which statement best accounts for pKa₁ being much lower than that of ethanoic acid and for pKa₂ being higher than pKa₁?
Answer: (A)
The acidity of a carboxylic acid depends on how stable its conjugate base is. In oxalic acid the second –COOH group is directly attached to the first and strongly withdraws electrons (–I effect). This stabilises the monoanion, so pKa₁ (1.25) is far below that of ethanoic acid (4.76). In the second step, H⁺ is removed from HOOC–COO⁻, which is already negatively charged. The Coulombic attraction and the added charge repulsion in the dianion make this less favourable, so pKa₂ (4.27) is higher than pKa₁. Only the first option gives both effects correctly.
Q7 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Which is the stronger acid in water: trifluoroacetic acid, CF3COOH, or ethanoic acid, CH3COOH?
Answer: (A)
The acidity of a carboxylic acid depends on the stability of its carboxylate ion. Electron-withdrawing groups such as halogens stabilise the anion by the -I effect, which raises acid strength. Fluorine is the most electronegative element, so the CF3 group is much more electron-withdrawing than the CH3 group. Therefore CF3COOH is a much stronger acid than CH3COOH, with pKa about 0.2 against about 4.8.
Q8 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Consider the acids (I) CH₃COOH, (II) ClCH₂COOH, (III) Cl₂CHCOOH and (IV) FCH₂COOH. What is the order of decreasing acid strength in water?
Answer: (C)
The electron-withdrawing inductive effect of a halogen stabilises the carboxylate ion. Two chlorine atoms do more than one halogen atom of either kind, and one fluorine does more than one chlorine. The pKa values are about 1.3 (Cl₂CHCOOH), 2.6 (FCH₂COOH), 2.9 (ClCH₂COOH) and 4.8 (CH₃COOH): III > IV > II > I.
Q9 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Benzaldehyde in which the aldehydic hydrogen is replaced by deuterium (C6H5–CDO) is heated with concentrated NaOH in ordinary water (H2O) until the Cannizzaro reaction is complete. Which pair correctly describes the products after acidification and ignoring exchange of O–H hydrogens?
Answer: (A)
Principle: the Cannizzaro reaction of an aldehyde with no α-hydrogen proceeds by hydroxide adding to C=O, then a hydride shift from this adduct to the C=O of a second aldehyde molecule. Step 1: OH– adds to C6H5–CDO to give C6H5–CD(O–)(OH). Step 2: the D leaves as D– and attacks the carbonyl carbon of another C6H5–CDO, giving C6H5–CD2–O–. The donor becomes the carboxylate C6H5COO– with no C-bound D. Step 3: protonation by water gives C6H5CD2OH, and acidification gives C6H5COOH. The alcohol carbon holds two D atoms and the water supplies no C–H.
Q10 · Chemistry · Aldehydes, Ketones and Carboxylic Acids
Which compound turns an acidified potassium dichromate solution from orange to green when warmed?
Answer: (A)
Principle: aldehydes have a hydrogen atom attached to the carbonyl carbon, and this hydrogen is easily removed, so aldehydes are oxidised to carboxylic acids by mild oxidising agents such as acidified dichromate. Ketones have no such hydrogen, so they are resistant to oxidation. Apply it: ethanal is the only aldehyde in the list, so it is the only compound that causes the orange-to-green colour change.
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All 138 real JEE Main questions from Aldehydes, Ketones and Carboxylic Acids.
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About Aldehydes, Ketones and Carboxylic Acids in JEE Main.
How many questions come from Aldehydes, Ketones and Carboxylic Acids in JEE Main?
Aldehydes, Ketones and Carboxylic Acids (Chemistry, Class 12) has been asked 138 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.2 questions a paper, 5% of all Chemistry questions. It is the 7th most-asked of 21 Chemistry chapters. The 2025 shifts had 20 from it in all.
Which topics of Aldehydes, Ketones and Carboxylic Acids are asked most in JEE Main?
Nucleophilic addition (70), Aldol and Cannizzaro (27), Tests to distinguish aldehydes and ketones (21), Acidity of carboxylic acids (20), counted over the papers from 2020–2025.
Is Aldehydes, Ketones and Carboxylic Acids important for JEE Main 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 7 of 21 in Chemistry; use that to decide how much time it gets, not whether to study it.
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