Questions on Aufbau Principle
20 Multiple-Choice Questions — Aufbau Principle
1. What does the Aufbau principle describe?
A) Electron spin direction
B) Order in which electrons fill atomic orbitals
C) Ionization energy trends
D) Nuclear decay process
E) Chemical bonding types
2. According to the Aufbau principle, electrons fill orbitals starting from:
A) The highest energy level
B) The lowest energy level
C) The middle energy level
D) Random orbitals
E) Only s orbitals
3. Which orbital fills first according to the Aufbau principle?
A) 2p
B) 1s
C) 3d
D) 4f
E) 2s
4. The Aufbau principle is based on minimizing:
A) Atomic radius
B) Electron spin
C) Total atomic energy
D) Number of neutrons
E) Nuclear charge
5. What is the maximum number of electrons that can occupy the 3p subshell?
A) 2
B) 6
C) 10
D) 14
E) 18
6. According to Aufbau principle, after the 4s orbital is filled, which orbital fills next?
A) 3d
B) 4p
C) 5s
D) 3p
E) 4d
7. Which principle works together with the Aufbau principle to determine electron configuration?
A) Dalton’s atomic theory
B) Heisenberg uncertainty principle
C) Pauli exclusion principle
D) Boyle’s law
E) Avogadro’s law
8. The Aufbau principle helps explain:
A) Electron configurations of atoms
B) Nuclear fusion
C) Rate of chemical reactions
D) Molecular geometry
E) Isotopic abundance
9. What is the correct order for filling the first four orbitals?
A) 1s, 2s, 2p, 3s
B) 2s, 1s, 3s, 2p
C) 1s, 2p, 3s, 2s
D) 3s, 2s, 1s, 2p
E) 2p, 1s, 2s, 3s
10. Why does the 4s orbital fill before the 3d orbital?
A) 4s has lower energy than 3d
B) 3d orbitals don’t exist
C) 3d orbitals fill only after 4p
D) 4s orbitals hold more electrons
E) It is random
11. Which subshell comes immediately after 3p in the Aufbau order?
A) 4s
B) 3d
C) 4p
D) 2p
E) 5s
12. According to the Aufbau principle, which electron configuration is correct for calcium (Ca, Z=20)?
A) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d²
B) 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
C) 1s² 2s² 2p⁶ 3s² 3p⁶ 4p²
D) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s¹
E) 1s² 2s² 2p⁶ 3s² 3p⁶ 4d²
13. Which of the following violates the Aufbau principle?
A) Filling orbitals in order of increasing energy
B) Filling the 4s orbital before the 3d orbital
C) Filling 3d before 4s orbital
D) Filling orbitals with only two electrons maximum
E) Pairing electrons with opposite spins
14. How does electron-electron repulsion affect the Aufbau filling order?
A) It reverses the order
B) It has no effect
C) It causes slight energy shifts but overall order remains
D) It forces all electrons into the same orbital
E) It causes electron loss
15. Which of the following correctly shows the energy sequence of orbitals filling?
A) 1s < 2s < 2p < 3s < 3p < 4s < 3d
B) 1s < 2p < 2s < 3p < 3s < 4s < 3d
C) 1s < 2s < 3s < 2p < 3p < 4s < 3d
D) 1s < 2s < 2p < 3p < 3s < 4s < 3d
E) 1s < 3s < 2s < 2p < 3p < 4s < 3d
16. Which quantum number primarily determines the order of orbital filling in the Aufbau principle?
A) Spin quantum number (ms)
B) Magnetic quantum number (ml)
C) Principal quantum number (n) and azimuthal quantum number (l) combined
D) Mass number (A)
E) Atomic number (Z)
17. How many electrons can the 4d subshell hold according to the Aufbau principle?
A) 2
B) 6
C) 10
D) 14
E) 18
18. According to the Aufbau principle, the electron configuration of oxygen (Z=8) ends with:
A) 2p⁴
B) 2s²
C) 1s²
D) 3p²
E) 3s²
19. The Aufbau principle is most useful for determining:
A) Molecular shapes
B) Electron configurations of ground-state atoms
C) Nuclear reactions
D) Reaction rates
E) Solubility of compounds
20. Which of these statements is true regarding the Aufbau principle?
A) Electrons fill orbitals randomly
B) Orbitals fill from highest to lowest energy
C) Electrons fill orbitals to achieve maximum total energy
D) Orbitals fill from lowest to highest energy
E) Only s orbitals are filled
- Questions on Heisenberg Uncertainty Principle
- Questions About Energy Levels
- Questions About Quantum Numbers
Answers with Explanations
1. B – The Aufbau principle explains how electrons fill orbitals starting from the lowest energy.
2. B – Electrons occupy the lowest energy orbitals first.
3. B – The 1s orbital fills before all others.
4. C – The principle minimizes the total energy of the atom.
5. B – Each p subshell has 3 orbitals × 2 electrons = 6 electrons max.
6. A – After filling 4s, electrons enter the 3d orbital.
7. C – The Pauli exclusion principle also governs electron configuration.
8. A – It predicts electron configurations.
9. A – This is the correct order of filling.
10. A – 4s orbital is lower in energy than 3d in neutral atoms.
11. A – 4s fills immediately after 3p.
12. B – Calcium's ground state configuration ends in 4s².
13. C – 3d fills after 4s, not before.
14. C – Electron repulsion slightly affects energy levels but doesn’t change order.
15. A – This sequence reflects the typical energy order of filling orbitals.
16. C – The sum of n + l determines orbital energy order.
17. C – d subshell can hold 10 electrons.
18. A – Oxygen ends with 2p⁴ electrons.
19. B – Useful for ground-state electron configurations.
20. D – Electrons fill orbitals from lowest to highest energy.
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