JEE (Main) · Chemistry, Class 11
Hydrocarbons: JEE Main PYQ, 2020–2025
Hydrocarbons (Chemistry, Class 11) has been asked 160 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.4 questions a paper, 6% of all Chemistry questions. It is the 3rd most-asked of 21 Chemistry chapters. The 2025 shifts had 27 from it in all. Last checked 28 October 2026.
Questions per year, all shifts
Year by year.
| Year | Questions |
|---|---|
| 2020 | 16in 14 papers |
| 2021 | 42in 26 papers |
| 2022 | 33in 24 papers |
| 2023 | 11in 12 papers |
| 2024 | 31in 18 papers |
| 2025 | 27in 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.
- Alkenes and alkynes76
- Electrophilic substitution and directive influence34
- Aromatic hydrocarbons30
- Alkanes15
- Conformations of ethane5
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10 Hydrocarbons 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 · Hydrocarbons
In ethane, the two hydrogen atoms one on each carbon are separated by a dihedral angle of 60°. Which term describes this relationship?
Answer: (A)
Adjacent-carbon substituent relationships are named by their dihedral angle. A dihedral of about 60° is gauche, 180° is anti, and 0° is syn (eclipsed). Since one hydrogen on the front carbon and one on the rear carbon are 60° apart in the staggered form, the correct term is gauche. Geminal describes substituents on the same carbon and is not relevant here.
Q2 · Chemistry · Hydrocarbons
Mononitration of the benzene ring (conc. HNO₃/conc. H₂SO₄) of which one of the following gives only ONE possible product?
Answer: (C)
The number of products depends on how many non-equivalent ring C–H positions there are. In o-xylene there are two types (positions 3 and 4). In m-xylene there are three types (2, 4 and 5). In toluene there are three types (ortho, meta, para). In p-xylene, by symmetry, all four ring hydrogens are equivalent, so only one mononitro product forms. The answer is p-xylene.
Q3 · Chemistry · Hydrocarbons
Ethane passes from its staggered to its eclipsed conformation by rotation about the C–C bond. Which statement correctly describes what happens during this process?
Answer: (A)
Conformers are arrangements that interconvert by rotation about a single bond without breaking any bond. The ethane C–C bond is a σ bond formed by head-on overlap of sp³ orbitals, and this overlap is symmetrical about the bond axis. Rotation therefore leaves the overlap unchanged, and the hybridisation, bond lengths and bond angles stay the same. The only change is the dihedral angle between C–H bonds on the two carbons. In the eclipsed form the electron clouds of these bonds are closest, so repulsion (torsional strain) is highest and stability is lowest.
Q4 · Chemistry · Hydrocarbons
Why can the carbon–carbon single bond of ethane rotate freely about its axis?
Answer: (A)
Rotation is possible because a sigma bond is symmetric about the bond axis. A pi bond, by contrast, requires parallel p orbitals, and rotating breaks that overlap. Ethane's C–C bond is sigma, so it rotates freely.
Q5 · Chemistry · Hydrocarbons
Ozonolysis of but-2-ene, followed by treatment with zinc and water, gives:
Answer: (A)
Ozonolysis cleaves the C=C bond and puts an oxygen on each carbon. But-2-ene, CH₃–CH=CH–CH₃, splits symmetrically into two molecules of CH₃CHO, ethanal.
Q6 · Chemistry · Hydrocarbons
Toluene is first heated to boiling with excess chlorine in bright sunlight until all the side-chain hydrogens are replaced. The product is then treated with chlorine in the presence of anhydrous FeCl₃ in the dark. Which compound is the major final product?
Answer: (A)
Two conditions control the site of reaction. Cl₂ with heat and light is a free-radical process and substitutes the benzylic hydrogens of toluene successively, so excess Cl₂ gives benzotrichloride, C₆H₅CCl₃. Cl₂ with FeCl₃ in the dark is electrophilic aromatic substitution on the ring. The substituent now on the ring is –CCl₃, whose three electronegative Cl atoms withdraw electrons by the –I effect. It is therefore a deactivating, meta-directing group, and the major product is 1-chloro-3-(trichloromethyl)benzene. Treating –CCl₃ as an o/p-directing alkyl group, stopping at –CH₂Cl, or calling the ring unreactive are the errors in the other options.
Q7 · Chemistry · Hydrocarbons
Ethene is passed into cold, dilute, alkaline potassium permanganate solution (Baeyer's reagent) at room temperature. What is the main organic product?
Answer: (A)
Principle: Baeyer's reagent (cold, dilute, alkaline KMnO4) oxidises an alkene only at the double bond, adding two OH groups to the same carbons. Applying it to ethene, CH2=CH2 becomes HOCH2-CH2OH, which is ethane-1,2-diol. Bond cleavage happens only under hot, concentrated or acidic conditions, which is a different reaction.
Q8 · Chemistry · Hydrocarbons
Which statement correctly explains why electrophilic substitution in nitrobenzene occurs mainly at the meta position?
Answer: (A)
In nitrobenzene the –NO₂ group withdraws electrons by the −R effect (delocalisation of ring π electrons into the N=O bond) and by the −I effect. The resonance structures show positive charge developing at the ortho and para carbons, but not at the meta carbons. The ortho and para positions are therefore more strongly deactivated towards an electrophile. The meta position is relatively the most electron-rich, although still less reactive than benzene, so substitution occurs there.
Q9 · Chemistry · Hydrocarbons
When ethyne is passed through a red-hot iron tube at 873 K, it undergoes cyclic polymerisation to benzene. 26.0 g of ethyne (C₂H₂, molar mass 26 g mol⁻¹) is passed through the tube and the conversion to benzene (C₆H₆, molar mass 78 g mol⁻¹) is 75%. What mass of benzene is formed?
Answer: (A)
The reaction is 3 C₂H₂ → C₆H₆. Moles of ethyne = 26.0/26 = 1.00 mol. Moles of benzene at 100% = 1.00/3 = 0.333 mol, which is 0.333 × 78 = 26 g. At 75% conversion the mass is 0.75 × 26 = 19.5 g.
Q10 · Chemistry · Hydrocarbons
Why can individual conformers of ethane not be separated and isolated at room temperature?
Answer: (A)
Conformers are different spatial arrangements produced by rotation about a single bond. Whether a conformer can be isolated depends on the energy barrier to interconversion compared with thermal energy, kT. Ethane's barrier is about 12 kJ mol⁻¹, far below what molecules routinely possess at room temperature, so the conformers interconvert almost instantly and cannot be separated.
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All 160 real JEE Main questions from Hydrocarbons.
The questions from the actual papers, with the official answer and an explanation for each — chapter by chapter, or as full timed papers.
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About Hydrocarbons in JEE Main.
How many questions come from Hydrocarbons in JEE Main?
Hydrocarbons (Chemistry, Class 11) has been asked 160 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.4 questions a paper, 6% of all Chemistry questions. It is the 3rd most-asked of 21 Chemistry chapters. The 2025 shifts had 27 from it in all.
Which topics of Hydrocarbons are asked most in JEE Main?
Alkenes and alkynes (76), Electrophilic substitution and directive influence (34), Aromatic hydrocarbons (30), Alkanes (15), counted over the papers from 2020–2025.
Is Hydrocarbons important for JEE Main 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 3 of 21 in Chemistry; use that to decide how much time it gets, not whether to study it.
Where can I solve Hydrocarbons JEE Main previous year questions?
On Nikaalle, free: sign up and practise every past JEE Main question from Hydrocarbons with an explanation for each, or sit the full papers timed. The ten questions on this page are our own, written in the same pattern.
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