NEET UG · Physics · Nuclei

Radioactive Decay: NEET previous year questions

9 questions in ten years of NEET, in 8 of 10 papers. Pattern: Every year. Here is how it is asked and which ideas come back.

Asked in 10 years: 9; about 0.8 per paper
Years asked: 8/10; last asked 2026
Chance of a question next paper: 64%; historical rate, how we compute it
Weighted estimate: 0.8; model; history: 0.9 a paper on average, typically 0–1

Key findings

01
Asked in 8 of 10 papers, 9 questions in all: #93 of 204 topics by ten-year total. It comes back every 1.3 years on average.
02
100% of its questions since 2018 tested an idea never asked before; none repeated an idea from the year before.
03
No idea in this topic has been asked twice: every question tested something new.
04
NEET has asked 8 of the 89 ideas in this topic; 79 have never been asked, directly or indirectly.
05
Mostly asked as numerical (67%); 78% easy, 0% hard, and down from 0.9 to 0.6 questions a paper since 2024.

Questions per year

Up to 2023: 0.9; per paper
Since 2024: 0.6; -0.3
Usual gap: 1.3 yrs; between papers asking it
Swing: ±0.5; questions, year to year

How it is asked

Difficulty, format and skill

Across all 9 questions on Radioactive Decay since 2017.

Difficulty

QUESTIONS

Easy7 · 78%
Medium2 · 22%
Hard0 · 0%

Format

Numerical · 6 Q67%
One-line MCQ · 3 Q33%

Skill tested

Calculation · 5 Q56%
Multi-step · 2 Q22%
Application · 1 Q11%
Recall · 1 Q11%

Repeats

New idea, or one asked before?

Each column is a paper. Blue questions tested an idea NEET had not asked before; navy ones went back to an idea from an earlier paper. 2017 is the first paper, so everything in it counts as new.

’17’18’19’20’21’22’23’24’25’26

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

Coverage of the topic

NEET has asked 8 of the 89 ideas in this topic. 79 have never been asked yet.

Asked directly8 · 9%
Touched inside another question2 · 2%
Never asked79 · 89%

Ideas come from Lumi’s syllabus map of NCERT. A never-asked idea is not a safe skip: most new questions come from exactly these.

Drill down

Idea, year, question

Every idea NEET tested in this topic, with its ten papers. Open one to read the questions.

ideaAskedShareYears’17’18’19’20’21’22’23’24’25’26

1 · 11%11%1/10
- 2021 · Q1
  A radioactive nucleus $\mathrm{^{A}_{Z}X}$ undergoes spontaneous decay in the sequence…
  mediumOne-line MCQNew idea
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10
1 · 11%11%1/10

Squares are the ten papers, 2017 to 2026; darker means more questions. Share is of the level above.

Ideas

Every idea inside this topic

9 different ideas were tested; none came more than once. Radioactive Decay Law is the foundation for 49 other ideas in the syllabus.

Decay Q-Value Calculation1×
numerical
Numerical · 6% next · foundation for 12
Balancing Nuclear Decay Equations1×
numerical
Numerical · 6% next
Half-Life and Decay Constant1×
numerical
Numerical · 4% next · foundation for 28
Beta Plus Decay Mechanism1×
complete a nuclear reaction equation
One-line MCQ · 4% next · foundation for 11
Alpha Emission Z and A Changes1×
identify decay particles from z changes
One-line MCQ · 4% next · foundation for 3
Fraction Remaining After n Half-lives1×
numerical
Numerical · 4% next · foundation for 4
Composition of Alpha Particles1×
definition recall of alpha particle
One-line MCQ · 4% next
Fraction Decayed vs Fraction Remaining1×
numerical
Numerical · 4% next
Radioactive Decay Law1×
numerical
Numerical · 4% next · foundation for 49

Idea	Times	Format	Chance next	Foundation for
Decay Q-Value Calculationnumerical	1	NumericalCalculation	6%	12 ideas
Balancing Nuclear Decay Equationsnumerical	1	NumericalMulti-step	6%	–
Half-Life and Decay Constantnumerical	1	NumericalCalculation	4%	28 ideas
Beta Plus Decay Mechanismcomplete a nuclear reaction equation	1	One-line MCQApplication	4%	11 ideas
Alpha Emission Z and A Changesidentify decay particles from z changes	1	One-line MCQMulti-step	4%	3 ideas
Fraction Remaining After n Half-livesnumerical	1	NumericalCalculation	4%	4 ideas
Composition of Alpha Particlesdefinition recall of alpha particle	1	One-line MCQRecall	4%	–
Fraction Decayed vs Fraction Remainingnumerical	1	NumericalCalculation	4%	–
Radioactive Decay Lawnumerical	1	NumericalCalculation	4%	49 ideas

Chance next is the historical rate at which an idea with this record came back in the following paper. It is low for every idea, which is why learning the topic beats memorising past questions. All repeated ideas

Every question

Radioactive Decay questions, year by year

The opening words of each question as it appeared in the official paper, with the idea it tested.

NEET 20261 question

Q7
Consider the following nuclear reaction : $^{238}\mathrm{U}\to{}^{234}\mathrm{Th}+{}^4\mathrm{He}$ Take masses of $^{238}$ U, $^{234}$ Th…
Idea: Decay Q-Value Calculation
New ideaEasyNumerical

NEET 20241 question

Q29
$^{290}_{82}X \xrightarrow{\alpha} Y \xrightarrow{e^+} Z \xrightarrow{\beta^-} P \xrightarrow{e^-} Q$ In the nuclear emission stated…
Idea: Balancing Nuclear Decay Equations
New ideaMediumNumerical

NEET 20231 question

Q28
The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to…
Idea: Half-Life and Decay Constant
New ideaEasyNumerical

NEET 20221 question

Q5
In the given nuclear reaction, the element X is : $\mathrm{^{22}_{11}Na \to X + e^{+} + \nu}$
Idea: Beta Plus Decay Mechanism
New ideaEasyOne-line MCQ

NEET 20212 questions

Q1
A radioactive nucleus $\mathrm{^{A}_{Z}X}$ undergoes spontaneous decay in the sequence…
Idea: Alpha Emission Z and A Changes
New ideaMediumOne-line MCQ
Q33
The half-life of a radioactive nuclide is 100 hours. The fraction of original activity that will remain after 150 hours would be :
Idea: Fraction Remaining After n Half-lives
New ideaEasyNumerical

NEET 20191 question

Q31
α-particle consists of :
Idea: Composition of Alpha Particles
New ideaEasyOne-line MCQ

NEET 20181 question

Q13
For a radioactive material, half-life is 10 minutes. If initially there are 600 number of nuclei, the time taken (in minutes) for the…
Idea: Fraction Decayed vs Fraction Remaining
New ideaEasyNumerical

NEET 20171 question

Q3
Radioactive material 'A' has decay constant '8 $\lambda$ ' and material 'B' has decay constant ' $\lambda$ '. Initially they have same number…
Idea: Radioactive Decay Law
EasyNumerical

Questions from the official NEET UG papers published by NTA (CBSE before 2019). Topic and idea tags, counts and notes are Lumi’s.