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Class XI · Chemistry

Atomic Structure: NEET MCQ practice

350 practice questions on Atomic Structure, each with an explanation. Practise them chapter by chapter in the GyaanLoop app.

350

Practice questions

200

Easy

135

Medium

15

Hard

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What Atomic Structure covers

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

  • Discovery of electron, proton, neutron
  • Bohr model of hydrogen atom, spectrum of hydrogen atom
  • de Broglie relationship, Heisenberg uncertainty principle
  • Quantum mechanical model of atom, quantum numbers
  • Shapes of s, p, d orbitals; Aufbau principle, Pauli exclusion principle, Hund's rule
  • Electronic configuration of elements, stability of half-filled and fully-filled orbitals

Sample questions on Atomic Structure

Try each one, then open the answer and explanation.

Question 1 · Practice question

The radioisotope N-13 which has a half-life of 10 min is used to image organs in the body. If the injected sample has an activity of 40 μCi (microcurie), what is the activity after 30 min?

  1. A.10μCi
  2. B.20μCi
  3. C.5 μCi
  4. D.2.5 μCi
Show answer

Answer: C. 5 μCi

After three half-lives (30 min ÷ 10 min each), the activity halves three times: 40 → 20 → 10 → 5 μCi, so the answer is 5 μCi. Distractor (a) 10 μCi would be after two half-lives only, and (b) 20 μCi after just one half-life; (d) 2.5 μCi would be after four half-lives, which is longer than 30 min.

Question 2 · Practice question

Naturally occurring potassium consists of 0.01% at 40 K which has a half-life of 1.28 x 10 9 yr. Activity of 1.00 g sample of KCl is

  1. A.8 x 10 17 yr -1
  2. B.4 x 10 8 yr -1
  3. C.4.37 x 10 8 yr -1
  4. D.2.286 x 10 -9 yr -1
Show answer

Answer: C. 4.37 x 10 8 yr -1

Activity is calculated using A = λN, where λ = ln2/t½, and N = number of ⁴⁰K atoms in the sample. First, find moles of KCl → atoms of total K → atoms of ⁴⁰K → multiply by λ. Option (c) is correct because it uses actual constants; (b) is close but approximate. The other options arise from skipping half-life decay constant or misplacing decimal powers.

Question 3 · Practice question

Direction (Q. Nos. 22-27) This section contains a passage describing theory, experiments, data, etc. Two questions related to the paragraph have been given. Each question has only one correct answer out of the given 4 options (a), (b), (c) and (d). Passage l Isotope of oxygen with mass number less than 16 undergoes β + -emission. Assume an equimolar mixture of 14 O and 15 O, Also t 50 ( 14 O)= 71s, t 50 ( 15 O)= 124s. Q. Ratio of rate constants of 14 O to 15 O is

  1. A.1.75
  2. B.0.573
  3. C.1.14
  4. D.0.873
Show answer

Answer: A. 1.75

The rate constant for radioactive decay is inversely proportional to half-life: k = ln2 / t½. Given half-lives 71 s and 124 s, the ratio k(14O)/k(15O) = 124/71 = 1.75. The tempting wrong options come from mistakenly taking the reciprocal (71/124 ≈ 0.573) or mis‑applying the formula.

Question 4 · Practice question

Angular nodes in 4s- suborbit is equal to radial nodes in

  1. A.3d
  2. B.2p
  3. C.Both (A) and (B)
  4. D.none of these
Show answer

Answer: C. Both (A) and (B)

Angular nodes for an orbital depend only on azimuthal quantum number (l): for s orbital (l=0), angular nodes = 0. Radial nodes formula is n − l − 1. For 3d (n=3, l=2) → n − l − 1 = 0; for 2p (n=2, l=1) → n − l − 1 = 0. So both match. A common mistake is thinking only one option works because radial nodes increase with n, but here both have zero radial nodes.

Question 5 · Practice question

The de Broglie wavelength associated with a ball of mass 200 g and moving at a speed of 5 metres/hour, is of the order of (h = 6.625 x 10 -34 J s) is

  1. A.10 -15 m
  2. B.10 -20 m
  3. C.10 -25 m
  4. D.10 -30 m
Show answer

Answer: D. 10 -30 m

Using λ = h/(mv) with mass 0.2 kg and speed ≈ 1.39×10⁻³ m/s gives λ ≈ 2.4×10⁻³⁰ m, so the order is 10⁻³⁰ m. Be careful to convert grams to kg and metres/hour to m/s correctly — a common mistake is forgetting these conversions and picking a wrong order of magnitude.

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