JEE (Main) · Chemistry, Class 11
Structure of Atom: JEE Main PYQ, 2020–2025
Structure of Atom (Chemistry, Class 11) has been asked 106 times in the 111 JEE (Main) shift papers from 2020–2025: about 1 questions a paper, 4% of all Chemistry questions. It is the 16th most-asked of 21 Chemistry chapters. The 2025 shifts had 13 from it in all. Last checked 28 October 2026.
Questions per year, all shifts
Year by year.
| Year | Questions |
|---|---|
| 2020 | 11in 14 papers |
| 2021 | 25in 26 papers |
| 2022 | 25in 24 papers |
| 2023 | 13in 12 papers |
| 2024 | 19in 18 papers |
| 2025 | 13in 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.
- Dual nature and uncertainty principle33
- Bohr model27
- Quantum numbers20
- Atomic orbitals16
- Electronic configuration10
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10 Structure of Atom 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 · Structure of Atom
The energy of the electron in the ground state of hydrogen is −13.6 eV. What is the energy of the electron in the n = 2 level of He⁺?
Answer: (C)
E = −13.6 × Z²/n² = −13.6 × 4/4 = −13.6 eV, the same as the ground state of hydrogen.
Q2 · Chemistry · Structure of Atom
How many electrons in a ground-state bromine atom (Z = 35) have the azimuthal quantum number l = 1?
Answer: (C)
The azimuthal quantum number l = 1 identifies p subshells. Write the ground-state configuration of Br (Z = 35): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁵. Check the total: 2+2+6+2+6+10+2+5 = 35. The p electrons are in 2p (6), 3p (6) and 4p (5), so the total is 6 + 6 + 5 = 17. The value of l depends only on the type of subshell, not on the shell number n, so all p electrons are counted.
Q3 · Chemistry · Structure of Atom
In the ground-state electronic configuration of a chromium atom (Z = 24), how many electrons have the same value of the spin quantum number mₛ as the 3d electrons (the 3d electrons themselves included)?
Answer: (A)
Ground-state Cr is [Ar]3d⁵4s¹, not 3d⁴4s². By Hund's rule of maximum multiplicity, all six electrons in the 3d and 4s orbitals are unpaired with parallel spins, so they share one mₛ value. The filled subshells 1s², 2s², 2p⁶, 3s², 3p⁶ hold 18 electrons, with 9 of each spin. Electrons with the same mₛ as the 3d electrons number 9 + 5 + 1 = 15.
Q4 · Chemistry · Structure of Atom
How many values of the magnetic quantum number m_l are possible for a d subshell?
Answer: (B)
The magnetic quantum number m_l ranges from −l to +l, including zero. For a subshell, the number of allowed m_l values equals the number of orbitals, 2l + 1. For a d subshell, l = 2, so there are 2(2) + 1 = 5 values. Each value corresponds to one of the five d orbitals.
Q5 · Chemistry · Structure of Atom
In the Bohr model, an electron of the He⁺ ion is in the n = 3 orbit. Taking the ground-state energy of hydrogen as −13.6 eV, what are the kinetic energy and the potential energy of the electron in this orbit?
Answer: (A)
First find the total energy of a hydrogen-like ion: E = −13.6 Z²/n² eV = −13.6 × 4/9 = −6.04 eV. In a Bohr orbit, the Coulomb force supplies the centripetal force, so mv²/r = kZe²/r². This gives KE = ½mv² = kZe²/2r, while PE = −kZe²/r. So PE = −2 KE and E = KE + PE = −KE. Hence KE = +6.04 eV and PE = 2E = −12.09 eV.
Q6 · Chemistry · Structure of Atom
In a He⁺ ion, Bohr's model is applied with the electron treated as a standing wave on its circular orbit. The orbit is the one whose circumference equals exactly 3 de Broglie wavelengths of the electron. Taking the ground-state energy of hydrogen as −13.6 eV, what is the energy of the electron in this orbit?
Answer: (A)
A stable Bohr orbit holds a whole number of de Broglie wavelengths: 2πr = nλ. With λ = h/mv this gives mvr = nh/2π, which is Bohr's quantisation rule. A circumference of 3λ therefore means n = 3. For a hydrogen-like ion, Eₙ = −13.6 Z²/n² eV. With Z = 2 and n = 3, E = −13.6 × 4/9 ≈ −6.04 eV.
Q7 · Chemistry · Structure of Atom
In Bohr's model, the electron in the ground state of the hydrogen atom moves with a speed of approximately what value?
Answer: (A)
Bohr's quantisation of angular momentum, mvr = nh/2π, together with the balance between Coulomb attraction and centripetal force, gives the speed in the nth orbit of hydrogen as v = 2.19 × 10⁶/n m s⁻¹. For the ground state, n = 1, so v ≈ 2.19 × 10⁶ m s⁻¹, which is about 1/137 of the speed of light.
Q8 · Chemistry · Structure of Atom
What is the maximum number of electrons in an atom that can have the quantum numbers n = 3 and mₗ = +1?
Answer: (B)
For n = 3 the allowed values are l = 0, 1, 2. The value mₗ = +1 requires l ≥ 1, so it occurs in one 3p orbital and one 3d orbital. Each orbital holds a maximum of 2 electrons (mₛ = ±½), so the total is 2 × 2 = 4.
Q9 · Chemistry · Structure of Atom
An isolated hydrogen atom at rest emits a photon of wavelength 656 nm (the H-α line). Treating the photon as carrying momentum h/λ, and taking the mass of the recoiling atom as 1.674 × 10⁻²⁷ kg, what is the recoil speed of the atom? (h = 6.626 × 10⁻³⁴ J s)
Answer: (A)
Principle: momentum is conserved, and a photon carries momentum p = h/λ. The atom starts at rest, so after emission it recoils with equal and opposite momentum. Step 1: p = 6.626×10⁻³⁴ / 656×10⁻⁹ = 1.01×10⁻²⁷ kg m s⁻¹. Step 2: v = p/m = 1.01×10⁻²⁷ / 1.674×10⁻²⁷ ≈ 0.60 m s⁻¹. Do not equate the photon energy to the atom's kinetic energy, because that energy comes from the atom's internal transition.
Q10 · Chemistry · Structure of Atom
What is the largest number of electrons the shell with principal quantum number n = 3 can hold?
Answer: (C)
n = 3 allows l = 0, 1, 2: the 3s, 3p and 3d subshells, holding 2 + 6 + 10 = 18 electrons (2n²).
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All 106 real JEE Main questions from Structure of Atom.
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 Structure of Atom in JEE Main.
How many questions come from Structure of Atom in JEE Main?
Structure of Atom (Chemistry, Class 11) has been asked 106 times in the 111 JEE (Main) shift papers from 2020–2025: about 1 questions a paper, 4% of all Chemistry questions. It is the 16th most-asked of 21 Chemistry chapters. The 2025 shifts had 13 from it in all.
Which topics of Structure of Atom are asked most in JEE Main?
Dual nature and uncertainty principle (33), Bohr model (27), Quantum numbers (20), Atomic orbitals (16), counted over the papers from 2020–2025.
Is Structure of Atom important for JEE Main 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 16 of 21 in Chemistry; use that to decide how much time it gets, not whether to study it.
Where can I solve Structure of Atom JEE Main previous year questions?
On Nikaalle, free: sign up and practise every past JEE Main question from Structure of Atom 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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