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Class XII · Physics

Atoms and Nuclei: NEET MCQ practice

200 practice questions on Atoms and Nuclei, each with an explanation. Practise them chapter by chapter in the GyaanLoop app.

200

Practice questions

128

Easy

67

Medium

5

Hard

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What Atoms and Nuclei covers

Topics in the NEET (UG) 2026–27 syllabus for this chapter.

  • Alpha-particle scattering experiment, Rutherford's model of atom
  • Bohr model, energy levels, hydrogen spectrum
  • Composition and size of nucleus, atomic masses, isotopes
  • Mass-energy relation, mass defect, binding energy per nucleon and its variation with mass number
  • Nuclear fission and fusion

Sample questions on Atoms and Nuclei

Try each one, then open the answer and explanation.

Question 1 · Practice question

Suppose potential energy between particle A and B at separation r is given by U = k ln r, where k is constant. For such hypothetical system, the ratio of energy difference between energy levels (n = 1 and n = 2) and (n = 2 and n = 4) is (The energy of a particle in n th level is –13.6/n 2 )

  1. A.1
  2. B.2
  3. C.1/2
  4. D.3
Show answer

Answer: A. 1

In the given system U = k ln r, force F = –dU/dr = –k/r. Using Bohr quantization mvr = nħ and force condition mv²/r = k/r, velocity is constant, radius rₙ ∝ n, so potential energy Uₙ = k ln n + constant. Hence energy Eₙ = constant + k ln n, and energy differences like ΔE₁₂ = k ln 2, ΔE₂₄ = k ln 2, giving ratio 1. The mention of –13.6/n² is a distractor; applying it gives ratio 4, which is not among the options.

Question 2 · Practice question

Q. In a crystal, the distance between two atoms is:

  1. A.A. 200 Å to 300 Å
  2. B.B. 2 Å to 3 micron
  3. C.C. 2 Å to 3 Å
  4. D.D. 2 mm to 3 mm
Show answer

Answer: C. C. 2 Å to 3 Å

In crystals, the typical separation between neighboring atoms is 2–3 Å (1 Å = 10⁻¹⁰ m), a standard recall from atomic sizes and crystal lattices. Options with 200–300 Å, microns, or millimeters are far too large — those correspond to macroscopic distances or larger structures, not interatomic spacing.

Question 3 · Practice question

Q. The maximum possible electrons in an orbit is:

  1. A.A. 8 (2s + 6p electrons)
  2. B.B. 8 (6s + 2p electrons)
  3. C.C. 8 (4s + 4p electrons)
  4. D.D. 8 (1s + 7p electrons)
Show answer

Answer: A. A. 8 (2s + 6p electrons)

For the second shell (n = 2), s subshell holds max 2 electrons and p subshell holds max 6 electrons, giving a total of 8 electrons — matching option A. The wrong options incorrectly assign more than 2 electrons to an s subshell or fewer than 6 to a full p subshell, violating the rules of electron capacity per subshell.

Question 4 · Practice question

Radioactive material has a half-life of 10 days. What fraction of the material would remain after 30 days?

  1. A.0.5
  2. B.0.25
  3. C.0.125
  4. D.0.33
Show answer

Answer: C. 0.125

Every 10 days, half the material decays, so after 30 days (3 half-lives), fraction remaining = (1/2)³ = 1/8 = 0.125. Option B (0.25) corresponds to 2 half-lives, and option A (0.5) is only 1 half-life — those come from mis-counting the number of half-lives.

Question 5 · Practice question

Which energy state of triply ionized beryllium (Be +++ ) has the same electron orbital radius as that of the ground state of hydrogen? Given Z for beryllium = 4

  1. A.n = 1
  2. B.n = 2
  3. C.n = 3
  4. D.n = 4
Show answer

Answer: B. n = 2

The Bohr radius formula r ∝ n²/Z shows that for hydrogen (Z=1, n=1) radius is a₀. For Be³⁺ (Z=4), setting n²/4 = 1 gives n=2. The ground‑state hydrogen radius is matched by the n=2 state of Be³⁺. Avoid choosing n=1 because smaller Z in denominator would give a smaller radius.

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