JEE Main · Physics · Nuclei

Fission and Fusion: JEE Main previous year questions

Name: Fission and Fusion: JEE Main previous year questions
Creator: Lumi

9 questions in the 108 JEE Main shifts Lumi analysed, in 3 of 8 years. Pattern: Frequent. 8 came in 2024–26. Here is how it is asked and which ideas come back.

Questions: 9; in 9 of 108 shifts
Years asked: 3/8; last asked 2025
Chance in a shift: 13%; calibrated model, how we compute it
Weighted estimate: 0.1; model; history: 0.1 a shift on average, typically 0.0–0.1

Key findings

01
Asked in 3 of 8 years with analysed shifts and in 9 of 108 shifts: 9 questions, #181 of 196 topics. The years that asked it were 2.5 apart on average. Last asked in 2025.
02
100% of its questions since 2020 tested an idea no earlier year had asked; none repeated an idea from the year before.
03
The most repeated idea is Nuclear Fission Mechanics, asked 2 times in 2 shifts (2024), most often as “identify emitted particle in fission reaction”.
04
JEE Main has asked 7 of the 52 ideas in this topic; 41 have never been asked, directly or inside another question.
05
Mostly asked as single correct (67%); 22% need a numerical answer, 22% are easy and 11% hard.
06
The skill tested most is calculation (33%), then multi-step (33%).

Questions a shift, year by year

Out of the 25 Physics 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: 0 in 24 shifts · 2022: 0 in 24 shifts · 2023: 0 in 12 shifts · 2024: 7 in 18 shifts · 2025: 1 in 8 shifts · 2026: 0 in 9 shifts.

Up to 2023: 0.0; a shift, of 25
Since 2024: 0.1; 0.1
Usual gap: 2.5 yrs; between years asking it
Shifts with it: 9/108; 8% of analysed shifts

How it is asked

Difficulty, format and skill

Across all 9 questions on Fission and Fusion since 2017.

Difficulty

QUESTIONS

261

Easy2 · 22%
Medium6 · 67%
Hard1 · 11%

Format

Single correct · 6 Q67%
Numerical value · 2 Q22%
Match the list · 1 Q11%

Skill tested

Calculation · 3 Q33%
Multi-step · 3 Q33%
Conceptual · 1 Q11%
Recall · 1 Q11%
Application · 1 Q11%

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.

’17’20’21’22’23’24’25’26

Idea asked for the first time
Idea asked in an earlier year

Coverage of the topic

JEE Main has asked 7 of the 52 ideas in this topic. 41 have never been asked yet.

741

Asked directly7 · 13%
Touched inside another question4 · 8%
Never asked41 · 79%

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

Idea, year, question

Every idea JEE Main tested in this topic, with its eight years. Open one to read the questions.

ideaAskedShareYears’17’20’21’22’23’24’25’26

Open2 · 22%22%1/82
- 4 Apr ’24 S1 · Q47
  Which of the following nuclear fragments corresponding to nuclear fission between neutron ( $^{1}_{0}\mathrm{n}$ ) and uranium isotope…
  easySingle correctNew idea
- 8 Apr ’24 S2 · Q48
  In a hypothetical fission reaction ${}_{92}X^{236} \rightarrow {}_{56}Y^{141} + {}_{36}Z^{92} + 3\mathbf{R}$ The identity of emitted…
  easySingle correctNew idea
Open2 · 22%22%1/82
Open1 · 11%11%1/8
Open1 · 11%11%1/8
Open1 · 11%11%1/8
Open1 · 11%11%1/8
Open1 · 11%11%1/8

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

7 different ideas were tested; 2 came more than once.

Nuclear Fission Mechanics2×
identify emitted particle in fission reaction
Single correct · 2 shifts
Q-Value of a Reaction2×
reaction rate from stellar power and q-value
Numerical value · 2 shifts · 2 numerical
Q-Value Sign Convention1×
match list on nuclear reaction types
Match the list · 1 shift
Energy Density Comparison1×
energy ratio fusion vs fission per mass
Single correct · 1 shift
Fission Fragment Kinematics1×
speed of fission fragments from mass defect
Single correct · 1 shift
Mass Defect to MeV Conversion1×
energy released from nuclear reaction masses
Single correct · 1 shift
Reactor Power Calculation1×
reactor power from fuel burnt
Single correct · 1 shift

Idea	Times	Shifts	Format	Numerical
Nuclear Fission Mechanicsidentify emitted particle in fission reaction	2	2	Single correctApplication	–
Q-Value of a Reactionreaction rate from stellar power and q-value	2	2	Numerical valueCalculation	2
Q-Value Sign Conventionmatch list on nuclear reaction types	1	1	Match the listConceptual	–
Energy Density Comparisonenergy ratio fusion vs fission per mass	1	1	Single correctMulti-step	–
Fission Fragment Kinematicsspeed of fission fragments from mass defect	1	1	Single correctMulti-step	–
Mass Defect to MeV Conversionenergy released from nuclear reaction masses	1	1	Single correctCalculation	–
Reactor Power Calculationreactor power from fuel burnt	1	1	Single correctCalculation	–

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

Fission and Fusion 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 20251 question in 1 shift

3 Apr, Shift 1Q44
Match the LIST-I with LIST-II LIST-I A.…
Idea: Q-Value Sign Convention
New ideaMediumMatch the list

JEE Main 20247 questions in 7 shifts

4 Apr, Shift 1Q47
Which of the following nuclear fragments corresponding to nuclear fission between neutron ( $^{1}_{0}\mathrm{n}$ ) and uranium isotope…
Idea: Nuclear Fission Mechanics
New ideaEasySingle correct
4 Apr, Shift 2Q51
The disintegration energy $Q$ for the nuclear fission of $^{235}U \to {}^{140}Ce + {}^{94}Zr + n$ is ________ MeV. Given atomic masses of…
Idea: Q-Value of a Reaction
New ideaMediumNumerical value
8 Apr, Shift 2Q48
In a hypothetical fission reaction ${}_{92}X^{236} \rightarrow {}_{56}Y^{141} + {}_{36}Z^{92} + 3\mathbf{R}$ The identity of emitted…
Idea: Nuclear Fission Mechanics
New ideaEasySingle correct
9 Apr, Shift 1Q60
A star has $100\%$ helium composition. It starts to convert three ${}^4\mathrm{He}$ into one ${}^{12}\mathrm{C}$ via triple alpha process…
Idea: Q-Value of a Reaction
New ideaHardNumerical value
9 Apr, Shift 2Q37
The energy released in the fusion of $2\ kg$ of hydrogen deep in the sun is $E_H$ and the energy released in the fission of $2\ kg$ of…
Idea: Energy Density Comparison
New ideaMediumSingle correct
29 Jan, Shift 1Q47
The explosive in a Hydrogen bomb is a mixture of ${}_1\mathrm{H}^2$ , ${}_1\mathrm{H}^3$ and ${}_3\mathrm{Li}^6$ in some condensed form.…
Idea: Mass Defect to MeV Conversion
New ideaMediumSingle correct
30 Jan, Shift 2Q47
In a nuclear fission reaction of an isotope of mass $M$ , three similar daughter nuclei of same mass are formed. The speed of a daughter…
Idea: Fission Fragment Kinematics
New ideaMediumSingle correct

JEE Main 20201 question in 1 shift

2 Sep, Shift 1Q18
In a reactor, 2 kg of $_{92}\mathrm{U}^{235}$ fuel is fully used up in 30 days. The energy released per fission is 200 MeV. Given that the…
Idea: Reactor Power Calculation
New ideaMediumSingle correct

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.