Structure of Atom is a Class 11 Chemistry chapter in the NEET (UG) syllabus. NEET720 has 657 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.
105
easy
476
medium
76
hard
Topics covered
EM radiation and photoelectric effect · Dual nature and uncertainty principle · Wave mechanics · Electromagnetic radiation and photoelectric effect · Bohr model and hydrogen spectrum · Dual nature and uncertainty · Quantum numbers and orbitals · Electronic configuration · Orbital shapes and nodes · Hydrogen-like species · Pauli exclusion principle · Photon energy · Isoelectronic species · Bohr radius · de Broglie wavelength of accelerated electron · Radial probability distribution · Dual nature of matter · Balmer series limit · Shielding effect · Photon count from power · (n+l) rule · Quantum numbers for f-orbitals · Photoelectric effect and de Broglie wavelength · Effective nuclear charge · Stopping potential · Orbital shapes · Spectral lines count · Atomic Spectra · Dual Behaviour of Matter · Bohr model and de Broglie hypothesis · Electronic configuration exceptions · Heisenberg uncertainty and orbital shape · Hund's rule and quantum numbers · Electronic configuration of ions · Magnetic moment and configuration · Bohr transitions · de Broglie hypothesis · Quantum numbers · Magnetic moment comparison · Bohr model limits
8 free Structure of Atom practice questions with answers
Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.
Question 1 · easy · Electronic configuration
Which statement correctly expresses the Pauli exclusion principle?
- A.Electrons occupy degenerate orbitals singly before pairing
- B.Orbitals are filled in order of increasing energy
- C.No two electrons in an atom can have identical values of all four quantum numbers
- D.An orbital can hold any number of electrons provided their spins differ
Show answer and explanation
Answer: C. No two electrons in an atom can have identical values of all four quantum numbers
Pauli's exclusion principle forbids two electrons in an atom from having the same set of all four quantum numbers, which limits an orbital to two electrons of opposite spin.
The Pauli exclusion principle states that no two electrons in the same atom can have identical values of n, l, m and s. Two electrons in one orbital share n, l and m, so they must differ in s (+1/2 and -1/2), capping orbital occupancy at two. Option A is Hund's rule, option B is the Aufbau principle, and option D wrongly extends the opposite-spin idea to unlimited occupancy since s has only two allowed values.
Common mistake: Confusing Pauli's principle with Hund's rule or Aufbau principle
Question 2 · medium · Electronic configuration
Hund's rule favours the singly occupied, parallel-spin arrangement in degenerate orbitals primarily because this arrangement
- A.minimises the nuclear charge experienced by each electron
- B.maximises exchange energy and minimises inter-electronic repulsion
- C.increases the total number of electrons the subshell can hold
- D.lowers the (n+l) value of the subshell
Show answer and explanation
Answer: B. maximises exchange energy and minimises inter-electronic repulsion
Electrons with parallel spins in separate degenerate orbitals gain maximum exchange energy stabilisation and stay farther apart, reducing coulombic repulsion.
Hund's rule of maximum multiplicity is grounded in two stabilising factors. First, parallel-spin electrons in different degenerate orbitals can exchange positions, and each such exchange pair releases exchange energy; the parallel arrangement maximises the number of exchange pairs. Second, singly occupying separate orbitals keeps electrons spatially apart, minimising coulombic repulsion compared to forced pairing in one orbital. Nuclear charge (A) and subshell capacity (C) are unaffected by spin arrangement, and (n+l) (D) governs the order of filling subshells, not the arrangement within one.
Common mistake: Treating Hund's rule as arbitrary rather than energy-based
Question 3 · medium · Electronic configuration
The Aufbau principle predicts the ground-state filling order of orbitals in an isolated multi-electron atom. It is best described as
- A.an exact law derived from the Schrodinger equation with no exceptions
- B.a rule that applies only to atoms with fewer than 18 electrons
- C.a rule for filling isolated hydrogen-like orbitals, unrelated to multi-electron energies
- D.an empirical guideline (via the (n+l) rule) that correctly predicts most, but not all, ground-state configurations
Show answer and explanation
Answer: D. an empirical guideline (via the (n+l) rule) that correctly predicts most, but not all, ground-state configurations
The Aufbau principle, operationalised through the (n+l) rule, correctly predicts the great majority of ground-state configurations but fails for elements like Cr and Cu where subtle exchange-energy effects intervene.
The (n+l) rule is an empirical ordering scheme, not an exact derivation from first principles for many-electron atoms (which cannot be solved exactly). It successfully predicts configurations for most elements by tracking how shielding and penetration change subshell energies as Z increases, but for a handful of elements (Cr, Cu, Mo, Ag, and several others outside the NEET syllabus) the true ground state deviates because of extra stabilisation from half-filled or fully-filled subshells. It is not restricted to any electron-count cutoff and is grounded in multi-electron energetics, not simple hydrogen-like orbital energies.
Common mistake: Treating the Aufbau principle as an exceptionless law
Question 4 · medium · Electronic configuration
Which of the following correctly links a configuration feature to the resulting bulk magnetic behaviour?
- A.All unpaired electrons in an atom → the substance is always ferromagnetic
- B.All electrons paired in every atom of the substance → diamagnetic, weakly repelled by a magnetic field
- C.Some unpaired electrons present → the substance is strongly attracted like iron metal
- D.Paired electrons in an atom always cause paramagnetism because paired spins reinforce a net moment
Show answer and explanation
Answer: B. All electrons paired in every atom of the substance → diamagnetic, weakly repelled by a magnetic field
A substance whose atoms/ions have all electrons paired shows no net atomic magnetic moment and is diamagnetic, weakly repelled by an external field.
Diamagnetism arises when every electron in the species is paired, so individual spin/orbital moments cancel, leaving no permanent atomic magnetic moment; such substances are weakly repelled by a magnetic field. Paramagnetism (option C exaggerates it) arises from unpaired electrons and is generally a weak attraction unless the substance is ferromagnetic (option A), which additionally requires long-range cooperative alignment of moments across a crystal lattice — a property of only a few metals (Fe, Co, Ni), not a guaranteed outcome of having unpaired electrons. Paired spins (option D) cancel rather than add.
Common mistake: Equating any paramagnetic species with ferromagnetic behaviour
Question 5 · easy · Electromagnetic radiation and photoelectric effect
Arrange the following regions of the electromagnetic spectrum in order of increasing frequency: (i) microwave (ii) ultraviolet (iii) visible (iv) FM radio wave
- A.(ii) < (iii) < (i) < (iv)
- B.(i) < (iv) < (iii) < (ii)
- C.(iv) < (i) < (iii) < (ii)
- D.(iv) < (iii) < (i) < (ii)
Show answer and explanation
Answer: C. (iv) < (i) < (iii) < (ii)
Frequency increases as wavelength decreases: radio < microwave < visible < ultraviolet.
In the electromagnetic spectrum, frequency rises in the order radio waves < microwaves < infrared < visible < ultraviolet < X-rays < gamma rays. FM radio waves have the lowest frequency here, followed by microwaves, then visible light, then ultraviolet. So the order is (iv) < (i) < (iii) < (ii), option C.
Common mistake: Confusing the wavelength order with the frequency order
Question 6 · medium · Quantum numbers and orbitals
When a transition metal atom such as iron loses electrons to form a cation, the electrons removed first come from the 4s orbital rather than 3d, even though 4s filled before 3d in the neutral atom. This is because:
- A.4s electrons are always higher in energy than 3d electrons, in both neutral atoms and ions
- B.once 3d starts filling, increasing nuclear charge lowers 3d energy below 4s in the resulting species, so 4s electrons are removed first on ionisation
- C.electrons are always removed in the reverse order of the (n+l) rule used for filling, as a universal law for every subshell pair
- D.3d electrons are more tightly bound only because they carry a formal negative charge, unlike 4s electrons
Show answer and explanation
Answer: B. once 3d starts filling, increasing nuclear charge lowers 3d energy below 4s in the resulting species, so 4s electrons are removed first on ionisation
As 3d fills and nuclear charge increases, poor shielding by other 3d electrons pulls 3d orbitals closer to the nucleus and below 4s in energy for the resulting cation, so 4s electrons ionise first.
In the neutral atom, 4s is filled before 3d because of penetration effects captured by the (n+l) rule. However, once 3d orbitals start gaining electrons, the increased effective nuclear charge is felt strongly by the poorly-shielding 3d electrons, pulling the 3d orbitals down in energy relative to 4s. By the time the atom or its cation is considered, 3d is actually lower in energy than 4s, so during ionisation the higher-energy 4s electrons are removed first (e.g. Fe: [Ar]3d⁶4s² → Fe²⁺: [Ar]3d⁶). This is a specific, experimentally observed 3d/4s crossover, not a universal reversal rule for all subshell pairs.
Common mistake: Assuming the filling order and the ionisation order must always be identical
Question 7 · easy · Bohr Model
Calculate the radius of the n = 3 orbit of the H species. (Radius of the first Bohr orbit of hydrogen = 0.529 A)
- A.4.761 A
- B.1.587 A
- C.0.1763 A
- D.14.28 A
Show answer and explanation
Answer: A. 4.761 A
r = 0.529 n^2/Z = 0.529 x 9/1 = 4.761 A.
For a hydrogen-like species the Bohr radius is r-n = 0.529 (n^2/Z) A, where Z is the nuclear charge. For H, Z = 1, and the orbit required has n = 3, so n^2 = 9. Substituting, r = 0.529 x 9/1 = 4.761 A. The radius grows as n^2 but shrinks as 1/Z, so a higher nuclear charge pulls the orbit closer to the nucleus.
Common mistake: Forgetting to divide by Z for hydrogen-like ions
Question 8 · easy · Bohr Model
Calculate the radius of the n = 2 orbit of the He+ species. (Radius of the first Bohr orbit of hydrogen = 0.529 A)
- A.0.529 A
- B.1.058 A
- C.4.232 A
- D.2.116 A
Show answer and explanation
Answer: B. 1.058 A
r = 0.529 n^2/Z = 0.529 x 4/2 = 1.058 A.
For a hydrogen-like species the Bohr radius is r-n = 0.529 (n^2/Z) A, where Z is the nuclear charge. For He+, Z = 2, and the orbit required has n = 2, so n^2 = 4. Substituting, r = 0.529 x 4/2 = 1.058 A. The radius grows as n^2 but shrinks as 1/Z, so a higher nuclear charge pulls the orbit closer to the nucleus.
Common mistake: Forgetting to divide by Z for hydrogen-like ions
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Questions about Structure of Atom for NEET
How many NEET questions does NEET720 have on Structure of Atom?＋
NEET720 has 657 reviewed practice questions on Structure of Atom (Chemistry): 105 easy, 476 medium and 76 hard. 8 of them are free on this page with full explanations; the rest are available in the app.
Is Structure of Atom a Class 11 or Class 12 chapter for NEET?＋
Structure of Atom is a Class 11 Chemistry chapter in the NEET (UG) syllabus. Read the NCERT chapter first, then practise chapter-wise MCQs and previous-year questions.
How should I practise Structure of Atom for NEET?＋
Attempt the questions below without looking at the options for more than a few seconds, mark your answer, then read the explanation even when you were right. Record every mistake and revisit it after a gap. On NEET720 this happens automatically: wrong answers go to your Mistake Book and are scheduled for spaced revision.
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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (657 active practice questions in this chapter today).