JEE (Advanced) · Physics, Class 12
Atoms and Nuclei: JEE Advanced PYQ, 2007–2026
Atoms and Nuclei (Physics, Class 12) has been asked 59 times in the 40 JEE (Advanced) papers from 2007–2026: about 1.5 questions a paper, 8% of all Physics questions. It is the 5th most-asked of 19 Physics chapters. The two 2026 papers had 2 from it. Last checked 28 October 2026.
Questions per year, both papers
Year by year.
| Year | Questions |
|---|---|
| 2007 | 4in 2 papers |
| 2008 | 6in 2 papers |
| 2009 | 3in 2 papers |
| 2010 | 3in 2 papers |
| 2011 | 2in 2 papers |
| 2012 | 2in 2 papers |
| 2013 | 5in 2 papers |
| 2014 | 1in 2 papers |
| 2015 | 6in 2 papers |
| 2016 | 5in 2 papers |
| 2017 | 2in 2 papers |
| 2018 | 2in 2 papers |
| 2019 | 3in 2 papers |
| 2020 | 1in 2 papers |
| 2021 | 3in 2 papers |
| 2022 | 3in 2 papers |
| 2023 | 2in 2 papers |
| 2024 | 2in 2 papers |
| 2025 | 2in 2 papers |
| 2026 | 2in 2 papers |
Each year has two papers, and the number of questions has fallen over time, so compare per paper and expect some drift.
Inside the chapter
Topics asked most.
- Radioactivity21
- Bohr model15
- Hydrogen spectrum10
- Nuclear fission and fusion8
- Nuclear binding energy5
Try it
10 Atoms and Nuclei questions to practise.
Our own questions, written in the JEE Advanced pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Physics · Atoms and Nuclei
A radioactive isotope has a half-life of 693 s. Taking ln 2 = 0.693, what is its decay constant?
Answer: (A)
The decay constant λ is related to the half-life by T½ = ln 2 / λ, so λ = ln 2 / T½. Substituting ln 2 = 0.693 and T½ = 693 s gives λ = 0.693 / 693 = 1.0 × 10⁻³ s⁻¹. The unit is s⁻¹, since λ is a rate of decay per nucleus per unit time.
Q2 · Physics · Atoms and Nuclei
Which statement about the decay constant λ of a radioactive nuclide is correct?
Answer: (A)
In the law dN/dt = −λN, λ is the probability per unit time that any one nucleus decays. The decay of any one nucleus is random, so this probability does not change with the age of the nucleus. It is a property of the nuclide, set by nuclear forces and unaffected by temperature, pressure or chemical state. The activity λN falls with time only because N falls.
Q3 · Physics · Atoms and Nuclei
Consider Rutherford's planetary model of a hydrogen atom, with the electron in a circular orbit of radius r about the proton under Coulomb attraction. According to classical electromagnetism, the accelerating electron radiates energy and spirals inward. Treating each stage as a nearly circular orbit, by what factor does the orbital frequency of the electron increase when the orbit radius shrinks from r to r/4?
Answer: (A)
For a circular orbit, ke²/r² = mv²/r, so v² = ke²/(mr) and v ∝ r^(-1/2). The orbital frequency is f = v/(2πr) ∝ r^(-3/2). When r becomes r/4, f increases by 4^(3/2) = 8. Because the frequency changes continuously as the electron spirals in, the classical model predicts a continuous spectrum and an unstable atom, which does not match the observed line spectrum.
Q4 · Physics · Atoms and Nuclei
Which unit is the SI unit of the activity of a radioactive source, defined as one disintegration per second?
Answer: (A)
Activity is the rate at which a sample's nuclei decay. Its SI unit is the becquerel, where 1 Bq = 1 disintegration per second. The curie is an older, non-SI unit. Gray and sievert are both units of radiation dose, which measure absorbed energy or biological effect, so they measure something different from activity.
Q5 · Physics · Atoms and Nuclei
A rock initially contained only a radioactive parent nuclide of half-life 2.0 × 10⁹ years. None of the daughter product was present at the start, the daughter is stable, and none has escaped. The rock is now found to contain daughter and parent nuclei in the ratio 7 : 1. The age of the rock is
Answer: (A)
Let the original number of parent nuclei be N₀. The parent plus daughter total is always N₀. If daughter : parent = 7 : 1, the parent left is N₀/8. Then (1/2)ⁿ = 1/8 gives n = 3 half-lives. The age is 3 × 2.0 × 10⁹ = 6.0 × 10⁹ years.
Q6 · Physics · Atoms and Nuclei
A radioactive nuclide X can decay by two independent modes. By α-emission alone its partial half-life would be 4 years, and by β⁻-emission alone its partial half-life would be 12 years. Both modes operate simultaneously on every nucleus. What is the effective half-life of X?
Answer: (A)
The decay probability per unit time of a nucleus is the sum of the probabilities for each independent mode, so λ = λ_α + λ_β. Since λ = ln2/T, this gives 1/T = 1/T_α + 1/T_β = 1/4 + 1/12 = 4/12 = 1/3, so T = 3 years. The effective half-life must be shorter than both partial half-lives, which rules out 6, 8 and 16 years.
Q7 · Physics · Atoms and Nuclei
A radioactive sample has activity A. If the number of undecayed nuclei is doubled while the decay constant stays the same, what happens to the activity?
Answer: (A)
The activity is A = -dN/dt = lambda N, the product of the decay constant and the number of undecayed nuclei. Since lambda is unchanged and N doubles, the activity doubles.
Q8 · Physics · Atoms and Nuclei
The total binding energies of ²³⁸U, ²³⁴Th and ⁴He are 1802 MeV, 1778 MeV and 28.3 MeV respectively. Using these, find the energy released (Q value) in the alpha decay ²³⁸U → ²³⁴Th + ⁴He.
Answer: (A)
Energy released equals the increase in total binding energy. Products: 1778 + 28.3 = 1806.3 MeV. Parent: 1802 MeV. Q = 1806.3 − 1802 = 4.3 MeV. It is positive, so the decay is energetically allowed.
Q9 · Physics · Atoms and Nuclei
The beta decay ¹⁴₆C → ¹⁴₇N + e⁻ + antineutrino occurs. The atomic masses are 14.003242 u for ¹⁴C and 14.003074 u for ¹⁴N. Using 1 u = 931.5 MeV/c² and mₑc² = 0.511 MeV, the maximum kinetic energy of the emitted electron (neglecting the recoil of the daughter) is closest to:
Answer: (A)
For β⁻ decay, ¹⁴C atom (6 electrons) → ¹⁴N atom (7 electrons, since 6 orbital electrons plus the emitted one is the same as 7 in the neutral atom) + antineutrino. The electron counts cancel, so Q = [M(¹⁴C) − M(¹⁴N)]c². Δm = 0.000168 u, so Q = 0.000168 × 931.5 = 0.156 MeV. This is the maximum electron kinetic energy when the recoil of the heavy daughter is neglected and the antineutrino carries almost no energy.
Q10 · Physics · Atoms and Nuclei
Which statement about gamma radiation emitted by a radioactive nucleus is correct?
Answer: (A)
Gamma emission is the release of a photon when a nucleus moves from an excited state to a lower one. Because no nucleons or protons leave the nucleus, the mass number and atomic number stay the same. Gamma rays are electromagnetic waves and carry no charge or mass.
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All 59 real JEE Advanced questions from Atoms and Nuclei.
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 Atoms and Nuclei in JEE Advanced.
How many questions come from Atoms and Nuclei in JEE Advanced?
Atoms and Nuclei (Physics, Class 12) has been asked 59 times in the 40 JEE (Advanced) papers from 2007–2026: about 1.5 questions a paper, 8% of all Physics questions. It is the 5th most-asked of 19 Physics chapters. The two 2026 papers had 2 from it.
Which topics of Atoms and Nuclei are asked most in JEE Advanced?
Radioactivity (21), Bohr model (15), Hydrogen spectrum (10), Nuclear fission and fusion (8), counted over the papers from 2007–2026.
Is Atoms and Nuclei important for JEE Advanced 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 5 of 19 in Physics; use that to decide how much time it gets, not whether to study it.
Where can I solve Atoms and Nuclei JEE Advanced previous year questions?
On Nikaalle, free: sign up and practise every past JEE Advanced question from Atoms and Nuclei 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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