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NEET Atomic Structure: 5 practice MCQs with answers

By the PrepMatic team · Updated 9 Oct 2026 · 4 min read

Atomic Structure is a Class 11 Chemistry chapter that mixes theory (models, quantum numbers) with direct questions on configurations and the hydrogen atom. The five MCQs below test shell capacity, the possible values of the magnetic quantum number, the electronic configuration of chromium, unpaired electrons in Fe³⁺ and the Bohr radius, at NCERT level.

What this chapter covers in the NEET syllabus

Atomic Structure is its own NMC unit and a Class 11 NCERT chapter. The topics are:

• Thomson, Rutherford and Bohr models, and the Bohr model of the hydrogen atom with its line spectrum.
• Dual behaviour of matter, the de Broglie relation and the Heisenberg uncertainty principle.
• The quantum mechanical model: orbitals, the four quantum numbers and the shapes of s, p and d orbitals.
• Rules for filling orbitals: the Aufbau principle, the Pauli exclusion principle and Hund's rule.
• Electronic configurations of atoms and ions, and the extra stability of half-filled and fully filled subshells.

Five practice MCQs on Atomic Structure

Question 1

The maximum number of electrons that can be accommodated in the shell with principal quantum number n = 3 is:

• A. 8
• B. 32
• C. 18
• D. 10

Question 2

For an electron with azimuthal quantum number l = 2, the number of possible values of the magnetic quantum number ml is:

• A. 3
• B. 5
• C. 7
• D. 9

Question 3

The ground-state electronic configuration of chromium (Z = 24) is:

• A. [Ar] 3d⁵ 4s¹
• B. [Ar] 3d⁴ 4s²
• C. [Ar] 3d⁶
• D. [Ar] 3d³ 4s² 4p¹

Question 4

The number of unpaired electrons in Fe³⁺ (Z = 26) is:

• A. 4
• B. 3
• C. 5
• D. 6

Question 5

The radius of the second Bohr orbit of hydrogen is how many times the radius of the first orbit?

• A. 8
• B. 2
• C. 1/4
• D. 4

Answers and explanations

1. C. The maximum number of electrons in a shell is 2n². For n = 3 this is 2 × 9 = 18 (2 in 3s, 6 in 3p and 10 in 3d). Option A is the capacity of the n = 2 shell, and B that of n = 4.
2. B. For a given l, ml takes the values −l to +l, which is 2l + 1 values. For l = 2 (d orbitals) these are −2, −1, 0, +1, +2, so there are 5.
3. A. Chromium prefers a half-filled d subshell, so one 4s electron moves to 3d: [Ar] 3d⁵ 4s¹. The same effect gives copper [Ar] 3d¹⁰ 4s¹. Option B is the regular Aufbau order, which chromium does not follow.
4. C. Neutral Fe is [Ar] 3d⁶ 4s². In forming Fe³⁺, the 4s electrons leave first and then one 3d electron, giving [Ar] 3d⁵. Five d electrons in five orbitals are all unpaired (Hund's rule).
5. D. In the Bohr model rn is proportional to n²/Z. For hydrogen r2/r1 = 2²/1² = 4. The first Bohr radius is 52.9 pm, so the second is about 211.6 pm.

How to prepare Atomic Structure

• Learn the four quantum numbers as a set of rules. n = 1, 2, 3...; l = 0 to n − 1; ml = −l to +l; ms = ±½. From them you can count orbitals (n² per shell, 2l + 1 per subshell) and electrons (2n² per shell).
• Practise writing configurations to Z = 30, then understand the two exceptions, chromium and copper. For cations, remove electrons from the outermost shell first (4s before 3d).
• Count unpaired electrons using Hund's rule. Fill each orbital of a subshell singly before pairing. Unpaired electron counts feed into magnetic moment and colour questions in the d-block and coordination chapters.
• Know the Bohr formulas. En = −13.6 Z²/n² eV and rn = 52.9 n²/Z pm. For the spectrum, 1/λ = RH Z² (1/n₁² − 1/n₂²), and learn which series (Lyman, Balmer, Paschen) lands on which level.
• Learn nodes. The number of radial nodes is n − l − 1 and angular nodes is l. A common question is how many nodes a 3p or 4d orbital has.
• Remember de Broglie and Heisenberg. λ = h/mv, and Δx · Δp is at least h/4π.

Ten focused problems a day on quantum numbers and configurations make this chapter easy marks. For wider planning see the NEET Chemistry preparation guide, and for the complete unit list the NEET syllabus.

Take a full Atomic Structure test on PrepMatic

Atomic Structure questions are quick when the rules are secure. Check yours with a PrepMatic topic test of about 15 questions in 30 minutes, scored with NEET's negative marking and included in the free Basic plan. For more chapters, use the practice hub.

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