JEE Main · Chemistry · Hydrocarbons
Alkanes and Free Radicals: JEE Main previous year questions
35 questions in the 108 JEE Main shifts Lumi analysed, in 7 of 8 years. Pattern: Asked most years. 15 came in 2024–26. Here is how it is asked and which ideas come back.
- Questions
- 35
- in 33 of 108 shifts
- Years asked
- 7/8
- last asked 2026
- Weighted estimate
- 0.3
- model; history: 0.3 a shift on average, typically 0.1–0.3
Key findings
- 01
Asked in 7 of 8 years with analysed shifts and in 33 of 108 shifts: 35 questions, #97 of 196 topics.
- 02
63% of its questions since 2020 tested an idea no earlier year had asked; 7 repeated an idea from the year before.
- 03
The most repeated idea is Wolff-Kishner Reduction to Alkanes, asked 4 times in 4 shifts (2021, 2023, 2024), most often as “predict product of reaction sequence”.
- 04
JEE Main has asked 18 of the 40 ideas in this topic; 21 have never been asked, directly or inside another question.
- 05
Mostly asked as diagram based (31%); 23% need a numerical answer, 26% are easy and 9% hard. It went up from 0.2 to 0.4 questions a shift since 2024.
- 06
The skill tested most is application (31%), then multi-step (31%).
Questions a shift, year by year
Out of the 25 Chemistry questions in a shift. Years differ in how many shifts Lumi analysed, so each year is scaled to one shift.
Raw count: 2017: 0 in 1 shift · 2020: 1 in 12 shifts · 2021: 10 in 24 shifts · 2022: 5 in 24 shifts · 2023: 4 in 12 shifts · 2024: 7 in 18 shifts · 2025: 2 in 8 shifts · 2026: 6 in 9 shifts.
- Up to 2023
- 0.2
- a shift, of 25
- Since 2024
- 0.4
- 0.2
- Usual gap
- 1.0 yrs
- between years asking it
- Shifts with it
- 33/108
- 31% of analysed shifts
How it is asked
Difficulty, format and skill
Across all 35 questions on Alkanes and Free Radicals since 2017.
Difficulty
QUESTIONS- Easy9 · 26%
- Medium23 · 66%
- Hard3 · 9%
Format
SHARE- Diagram based · 11 Q31%
- Single correct · 8 Q23%
- Numerical value · 8 Q23%
- Other · 4 Q11%
- Two statements · 3 Q9%
- Assertion–reason · 1 Q3%
Skill tested
SHARE- Application · 11 Q31%
- Multi-step · 11 Q31%
- Conceptual · 5 Q14%
- Calculation · 3 Q9%
- Recall · 3 Q9%
- Diagram reading · 2 Q6%
Repeats
New idea, or one asked before?
Each column is a year. Blue questions tested an idea no earlier year had asked; navy ones went back to an idea from an earlier year. 2017 is the first year, so everything in it counts as new. Heights are question counts, and Lumi analysed 1 to 24 shifts a year, so compare the split inside a column rather than heights across years.
- Idea asked for the first time
- Idea asked in an earlier year
Coverage of the topic
JEE Main has asked 18 of the 40 ideas in this topic. 21 have never been asked yet.
- Asked directly18 · 45%
- Touched inside another question1 · 3%
- Never asked21 · 53%
Ideas come from Lumi’s JEE syllabus map. A never-asked idea is not a safe skip: across all of JEE Main, 22% of questions since 2024 tested an idea no earlier year had asked.
Drill down
Chapter, idea, question
Every idea JEE Main tested in this topic, with its eight years. Open one to read the questions.
11 ideas inside
Squares are the 8 years with analysed shifts, 2017 to 2026. A number is the questions that year when there is more than one; the shade is scaled to one shift, so a year with more analysed shifts (1 to 24 a year) does not look darker. Share is of the level above.
Ideas
Every idea inside this topic
18 different ideas were tested; 11 came more than once.
predict product of reaction sequence
Diagram based · 4 shiftscount dichloro products of alkane
Diagram based · 3 shifts · 1 numericalzn-hg/hcl reduces both cho and c=o to alkyl groups, pick drawn product
Other · 3 shiftsmass of alkane from grignard protonation
Diagram based · 3 shifts · 1 numericaldihedral angle in staggered conformation
Diagram based · 3 shiftsidentify compound from reforming products
Diagram based · 2 shiftsformula of alkane from oxygen needed
Numerical value · 2 shifts · 2 numericalidentify compounds in reaction sequence
Numerical value · 2 shifts · 1 numericalstatement i/ii on methane preparation
Numerical value · 2 shifts · 1 numericalcount monochlorination isomers of 2-methylbutane
Numerical value · 2 shifts · 2 numericalclemmensen reduction then cr2o3 aromatization
Diagram based · 2 shiftsorder of radical stability at labelled carbons
Single correct · 1 shiftstatement i/ii on alkane properties
Two statements · 1 shiftmajor product of reaction sequence
Single correct · 1 shiftpredict product of reaction sequence
Single correct · 1 shiftcatalytic oxidation of propane to aldehyde
Single correct · 1 shiftstatement i/ii on oxidation of alkanes
Two statements · 1 shiftpredict product of reaction
Single correct · 1 shift
| Idea | Years asked | Times | Shifts | Format | Numerical |
|---|---|---|---|---|---|
| Wolff-Kishner Reduction to Alkanespredict product of reaction sequence | 4 | 4 | Diagram basedApplication | – | |
| Halogenation Chain Mechanismcount dichloro products of alkane | 3 | 3 | Diagram basedApplication | 1 | |
| Clemmensen Reduction to Alkaneszn-hg/hcl reduces both cho and c=o to alkyl groups, pick drawn product | 3 | 3 | OtherMulti-step | – | |
| Alkane Synthesis via Grignard Protonationmass of alkane from grignard protonation | 3 | 3 | Diagram basedApplication | 1 | |
| Ethane and Butane Conformersdihedral angle in staggered conformation | 3 | 3 | Diagram basedDiagram reading | – | |
| Catalytic Isomerization of Alkanesidentify compound from reforming products | 2 | 2 | Diagram basedApplication | – | |
| General Stoichiometry of Alkane Combustionformula of alkane from oxygen needed | 2 | 2 | Numerical valueCalculation | 2 | |
| Hydrolysis of Grignard Reagentsidentify compounds in reaction sequence | 2 | 2 | Numerical valueMulti-step | 1 | |
| Kolbe's Electrolytic Methodstatement i/ii on methane preparation | 2 | 2 | Numerical valueApplication | 1 | |
| Stereochemistry of Free Radical Halogenationcount monochlorination isomers of 2-methylbutane | 2 | 2 | Numerical valueCalculation | 2 | |
| Aromatization (Reforming) of Alkanesclemmensen reduction then cr2o3 aromatization | 2 | 2 | Diagram basedApplication | – | |
| Free Radical Stability Trendsorder of radical stability at labelled carbons | 1 | 1 | Single correctConceptual | – | |
| Melting Point Alternation Effectstatement i/ii on alkane properties | 1 | 1 | Two statementsConceptual | – | |
| Soda-Lime Decarboxylation of Carboxylic Acidsmajor product of reaction sequence | 1 | 1 | Single correctMulti-step | – | |
| Wurtz Reaction Limitationspredict product of reaction sequence | 1 | 1 | Single correctMulti-step | – | |
| Controlled Oxidation Catalystscatalytic oxidation of propane to aldehyde | 1 | 1 | Single correctRecall | – | |
| KMnO4 Oxidation of Tertiary Alkanesstatement i/ii on oxidation of alkanes | 1 | 1 | Two statementsConceptual | – | |
| Reactivity-Selectivity Principlepredict product of reaction | 1 | 1 | Single correctApplication | – |
Times and shifts count every analysed shift. Across JEE Main, 78% of questions since 2024 went back to an idea an earlier year had asked; the rest were new. All repeated ideas
Every question
Alkanes and Free Radicals questions, year by year
The opening words of each question as it appeared in the official paper, with the idea it tested. Open one for its options and the official answer.
JEE Main 20266 questions in 6 shifts
- 2 Apr, Shift 1Q73One mole of an alkane (x) requires mole oxygen for complete combustion. Sum of number of carbon and hydrogen atoms in the alkane (x)…
Idea: General Stoichiometry of Alkane Combustion
New ideaEasyNumerical value - 2 Apr, Shift 2Q64The compound (X) on heating in the presence of anhydrous AlCl and HCl gas gives 2,4-dimethyl pentane (ii) aromatization gives toluene…
Idea: Catalytic Isomerization of Alkanes
EasySingle correct - 5 Apr, Shift 2Q72RMgI when treated with ice cold water liberated a gas which occupied 1.4 dm/g at STP. The gas produced is further reacted with iodine…
Idea: Hydrolysis of Grignard Reagents
MediumNumerical value - 6 Apr, Shift 1Q65Given below are two statements: Statement I: Methane can be prepared by decarboxylation of sodium ethanoate, Kolbe's electrolysis of…
Idea: Kolbe's Electrolytic Method
MediumTwo statements - 6 Apr, Shift 2Q72An alkane (Y) requires 8 moles of oxygen for complete combustion and on chlorination with , (Y) gives only one…
Idea: General Stoichiometry of Alkane Combustion
New ideaMediumNumerical value - 8 Apr, Shift 2Q65n-Butane on monochlorination under photochemical condition gives an optically active compound "P". "P" on further chlorination gives…
Idea: Halogenation Chain Mechanism
MediumSingle correct
JEE Main 20252 questions in 2 shifts
- 2 Apr, Shift 1Q64Consider the following compound (X) with the carbons numbered I (the terminal C-H…
Idea: Free Radical Stability Trends
New ideaMediumSingle correct · figure - 2 Apr, Shift 2Q66Given below are two statements : Statement (I) : Neopentane forms only one monosubstituted derivative. Statement (II) : Melting point of…
Idea: Melting Point Alternation Effect
New ideaMediumTwo statements
JEE Main 20247 questions in 7 shifts
- 4 Apr, Shift 1Q79Identify the product in the following reaction : [reactant: benzene ring with a CHO group and, meta to it, a COCH3 group…
Idea: Clemmensen Reduction to Alkanes
Asked the year beforeEasyOther · figure - 5 Apr, Shift 1Q79Identify 'A' in the following reaction : butan-2-one ()…
Idea: Wolff-Kishner Reduction to Alkanes
Asked the year beforeEasyDiagram based · figure - 5 Apr, Shift 2Q78P Consider the…
Idea: Soda-Lime Decarboxylation of Carboxylic Acids
New ideaMediumSingle correct - 9 Apr, Shift 1Q74In the following sequence of reaction, the major products B and C respectively are : [figure: Cl-cyclobutane-Br (1,3-disubstituted…
Idea: Wurtz Reaction Limitations
New ideaHardSingle correct · figure - 1 Feb, Shift 2Q88Total number of isomeric compounds (including stereoisomers) formed by monochlorination of 2-methylbutane is ________.
Idea: Stereochemistry of Free Radical Halogenation
MediumNumerical value - 29 Jan, Shift 1Q76The final product A formed in the following multistep reaction sequence is
Idea: Wolff-Kishner Reduction to Alkanes
Asked the year beforeMediumDiagram based · figure - 31 Jan, Shift 1Q87Number of alkanes obtained on electrolysis of a mixture of and is _________.
Idea: Kolbe's Electrolytic Method
New ideaMediumNumerical value
JEE Main 20234 questions in 3 shifts
- 6 Apr, Shift 1Q89Number of bromo derivatives obtained on treating ethane with excess of in diffused sunlight is ________
Idea: Halogenation Chain Mechanism
Asked the year beforeHardNumerical value - 11 Apr, Shift 2Q76The major product formed in the following reaction is …
Idea: Clemmensen Reduction to Alkanes
Asked the year beforeMediumOther · figure - 11 Apr, Shift 2Q77Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : [figure: skeletal…
Idea: Wolff-Kishner Reduction to Alkanes
MediumAssertion–reason · figure - 13 Apr, Shift 1Q74In the following reaction 'X' is 'X' (major product)
Idea: Catalytic Isomerization of Alkanes
New ideaMediumDiagram based · figure
JEE Main 20225 questions in 5 shifts
- 25 Jul, Shift 2Q76--(, Ether)--> A --()--> B --(Zn-Hg, HCl)--> C The correct structure of C is
Idea: Clemmensen Reduction to Alkanes
New ideaMediumOther - 26 Jul, Shift 2Q89A 100 mL solution of on treatment with methanol produces 2.24 mL of a gas at STP. The weight of gas produced is…
Idea: Alkane Synthesis via Grignard Protonation
Asked the year beforeEasyNumerical value - 29 Jul, Shift 2Q74Compound ‘A’ undergoes following sequence of reactions to give compound ‘B’. The correct structure and chirality of compound ‘B’ is [where…
Idea: Hydrolysis of Grignard Reagents
New ideaMediumSingle correct · figure - 25 Jun, Shift 1Q72In the following structures, which one is having staggered conformation with maximum dihedral angle ?
Idea: Ethane and Butane Conformers
Asked the year beforeEasyDiagram based · figure - 28 Jun, Shift 2Q75A 4-Bromophenyl acetic acid. In the above…
Idea: Halogenation Chain Mechanism
New ideaMediumDiagram based · figure
JEE Main 202110 questions in 9 shifts
- 3 Aug, Shift 1Q50Which of the following is the most stable conformer?
Idea: Ethane and Butane Conformers
New ideaMediumDiagram based · figure - 26 Aug, Shift 1Q42Excess of isobutane on reaction with in presence of light at 125℃ gives which one of the following, as the major product ?
Idea: Reactivity-Selectivity Principle
New ideaEasySingle correct · figure - 27 Aug, Shift 1Q43In the following sequence of reactions the P is : [ring structure with Cl drawn] + Mg [ A ]…
Idea: Alkane Synthesis via Grignard Protonation
New ideaEasyDiagram based · figure - 31 Aug, Shift 2Q42Arrange the following conformational isomers of n-butane in order of their increasing potential energy : [four Newman projections labelled…
Idea: Ethane and Butane Conformers
New ideaMediumDiagram based · figure - 31 Aug, Shift 2Q43For the following sequence of reactions, the correct products are : [benzene ring drawn with alternating double bonds] 1. Br2/Fe/…
Idea: Alkane Synthesis via Grignard Protonation
New ideaMediumDiagram based · figure - 24 Feb, Shift 1Q42Which of the following reagent is used for the following reaction ?
Idea: Controlled Oxidation Catalysts
New ideaEasySingle correct - 24 Feb, Shift 2Q46[Reaction scheme: reactant product] Which of the following reagent is suitable for the preparation of the product in the…
Idea: Wolff-Kishner Reduction to Alkanes
New ideaMediumDiagram based · figure - 25 Feb, Shift 1Q43Identify A in the given chemical reaction.
Idea: Aromatization (Reforming) of Alkanes
New ideaMediumDiagram based · figure - 26 Feb, Shift 2Q42[reaction scheme: structure drawn in line-bond form]…
Idea: Aromatization (Reforming) of Alkanes
New ideaMediumOther · figure - 17 Mar, Shift 2Q44Given below are two statements : Statement I : 2-methylbutane on oxidation with gives 2-methylbutan-2-ol. Statement II :…
Idea: KMnO4 Oxidation of Tertiary Alkanes
New ideaMediumTwo statements
JEE Main 20201 question in 1 shift
- 3 Sep, Shift 1Q50The total number of monohalogenated organic products (including stereoisomers) in the following reaction is __________. A…
Idea: Stereochemistry of Free Radical Halogenation
New ideaHardNumerical value
Questions from the official JEE Main Paper 1 shifts published by NTA (CBSE for 2017). Questions NTA dropped are left out. Topic and idea tags, counts and notes are Lumi’s.