Structure of Atom MCQs – CBSE Class 11 Chemistry
Structure of Atom MCQs – CBSE Class 11 Chemistry
Course: CBSE Class 11 Chemistry – MCQs with Answers and Explanations
Section: Physical Chemistry – MCQ Titles
The following 50 Multiple Choice Questions (MCQs) are strictly based on the NCERT syllabus and structured section-wise to cover the complete framework of the Structure of Atom chapter. Each question is accompanied by the correct answer and a clear, concept-building explanation, making it ideal for CBSE board exam preparation.
Section A: Discovery of Sub-Atomic Particles
1. The discovery of electron was made by
A. Rutherford
B. Goldstein
C. J.J. Thomson
D. Chadwick
Answer: C
Explanation: J.J. Thomson discovered the electron through cathode ray experiments.
2. The charge to mass ratio of electron was determined by
A. Millikan
B. Rutherford
C. Thomson
D. Chadwick
Answer: C
Explanation: Thomson measured the e/m ratio of electrons using cathode rays.
3. The charge on an electron was measured by
A. Thomson
B. Millikan
C. Rutherford
D. Bohr
Answer: B
Explanation: Millikan’s oil drop experiment determined the charge of an electron.
4. Which particle was discovered using canal rays?
A. Electron
B. Neutron
C. Proton
D. Positron
Answer: C
Explanation: Goldstein discovered protons using canal rays.
Section B: Atomic Models
5. According to Thomson’s atomic model, atom is
A. solid sphere
B. hollow sphere
C. positively charged sphere with embedded electrons
D. nucleus with orbiting electrons
Answer: C
Explanation: Thomson proposed the plum pudding model.
6. Which observation disproved Thomson’s atomic model?
A. Line spectra
B. Photoelectric effect
C. Alpha particle scattering
D. Discovery of neutron
Answer: C
Explanation: Rutherford’s scattering experiment showed a dense nucleus.
7. Rutherford’s model failed to explain
A. existence of nucleus
B. stability of atom
C. positive charge
D. mass of nucleus
Answer: B
Explanation: According to classical physics, orbiting electrons should collapse.
8. In Rutherford’s experiment, most alpha particles passed undeflected because
A. nucleus is heavy
B. atom is mostly empty space
C. electrons are light
D. nucleus is negatively charged
Answer: B
Explanation: The atom has large empty space.
Section C: Atomic Number and Mass Number
9. Atomic number of an element represents the number of
A. neutrons
B. protons
C. electrons + neutrons
D. nucleons
Answer: B
Explanation: Atomic number equals the number of protons.
10. Mass number is equal to
A. protons + electrons
B. neutrons only
C. protons + neutrons
D. electrons only
Answer: C
Explanation: Mass number is the total number of nucleons.
11. Isotopes have
A. same mass number
B. same atomic number
C. same number of neutrons
D. different chemical properties
Answer: B
Explanation: Isotopes differ in neutrons but have same atomic number.
12. Isobars have
A. same atomic number
B. same number of neutrons
C. same mass number
D. same electronic configuration
Answer: C
Explanation: Isobars have same mass number but different atomic numbers.
Section D: Bohr’s Atomic Model
13. Bohr’s model is applicable to
A. all atoms
B. multi-electron atoms
C. hydrogen and hydrogen-like species
D. molecules
Answer: C
Explanation: Bohr’s model works only for single-electron systems.
14. According to Bohr, electrons revolve in
A. elliptical orbits
B. circular stationary orbits
C. random paths
D. spiral paths
Answer: B
Explanation: Bohr proposed fixed energy orbits.
15. The angular momentum of electron is quantized as
A. mv²
B. mvr = nh/2π
C. mv = h
D. mgh
Answer: B
Explanation: Bohr’s quantization condition.
16. Energy of electron in hydrogen atom depends on
A. size of nucleus
B. shape of orbit
C. principal quantum number
D. azimuthal quantum number
Answer: C
Explanation: Energy depends only on principal quantum number (n).
17. When an electron jumps from higher to lower energy level, energy is
A. absorbed
B. emitted
C. unchanged
D. destroyed
Answer: B
Explanation: Energy is released as radiation.
Section E: Quantum Mechanical Model
18. Dual nature of matter was proposed by
A. Einstein
B. Planck
C. de Broglie
D. Bohr
Answer: C
Explanation: de Broglie proposed wave nature of particles.
19. de Broglie wavelength is inversely proportional to
A. velocity
B. mass
C. momentum
D. energy
Answer: C
Explanation: λ = h / mv (momentum).
20. Heisenberg’s uncertainty principle states that
A. position and momentum cannot be measured simultaneously
B. electron follows circular path
C. energy is quantized
D. electrons emit radiation
Answer: A
Explanation: Exact position and momentum cannot be determined together.
21. Which equation represents the wave nature of electron?
A. Schrödinger equation
B. Newton’s equation
C. Planck’s equation
D. Einstein’s equation
Answer: A
Explanation: Schrödinger equation describes wave behaviour.
Section F: Quantum Numbers
22. Principal quantum number determines
A. shape of orbital
B. orientation
C. energy and size
D. spin
Answer: C
Explanation: It indicates energy level and orbital size.
23. Azimuthal quantum number (l) determines
A. energy only
B. shape of orbital
C. orientation
D. spin
Answer: B
Explanation: l defines the shape of orbitals.
24. Maximum value of l for n = 3 is
A. 1
B. 2
C. 3
D. 4
Answer: B
Explanation: l = n − 1 = 2.
25. Magnetic quantum number (mₗ) represents
A. energy
B. shape
C. orientation
D. size
Answer: C
Explanation: It defines orientation of orbital in space.
26. Spin quantum number has values
A. +1 and −1
B. 0 and 1
C. +½ and −½
D. +2 and −2
Answer: C
Explanation: Electron spin can be +½ or −½.
Section G: Orbitals and Electronic Configuration
27. Number of orbitals in p-subshell is
A. 1
B. 2
C. 3
D. 6
Answer: C
Explanation: p-subshell has three orbitals.
28. Maximum electrons in an s-orbital is
A. 1
B. 2
C. 6
D. 10
Answer: B
Explanation: One orbital can hold maximum two electrons.
29. Shape of p-orbital is
A. spherical
B. dumbbell
C. circular
D. linear
Answer: B
Explanation: p-orbitals are dumbbell-shaped.
30. The order of energy of orbitals is
A. 3s < 3p < 4s
B. 3s < 4s < 3p
C. 4s < 3p < 3s
D. 3p < 3s < 4s
Answer: B
Explanation: Based on (n + l) rule.
Section H: Electronic Configuration Principles
31. Aufbau principle is based on
A. Hund’s rule
B. Pauli exclusion principle
C. increasing orbital energy
D. electron pairing
Answer: C
Explanation: Electrons fill lowest energy orbitals first.
32. Pauli exclusion principle states
A. electrons pair first
B. no two electrons have same set of quantum numbers
C. orbitals degenerate
D. energy is quantized
Answer: B
Explanation: Each electron has unique quantum numbers.
33. Hund’s rule explains
A. orbital filling order
B. electron pairing
C. maximum multiplicity
D. wave nature
Answer: C
Explanation: Electrons occupy degenerate orbitals singly first.
34. Electronic configuration of nitrogen is
A. 1s² 2s² 2p²
B. 1s² 2s² 2p³
C. 1s² 2s² 2p⁴
D. 1s² 2s² 2p⁵
Answer: B
Explanation: Nitrogen has 7 electrons.
Section I: Spectra and Applications
35. Line spectrum of hydrogen arises due to
A. continuous energy levels
B. transition between fixed energy levels
C. nuclear reactions
D. electron spin
Answer: B
Explanation: Discrete transitions give line spectra.
36. Lyman series lies in
A. visible region
B. ultraviolet region
C. infrared region
D. X-ray region
Answer: B
Explanation: Lyman series appears in UV region.
37. Balmer series corresponds to transitions ending at
A. n = 1
B. n = 2
C. n = 3
D. n = 4
Answer: B
Explanation: Balmer series ends at n = 2.
Section J: Conceptual NCERT-Based MCQs
38. Which model introduced quantization of energy?
A. Thomson
B. Rutherford
C. Bohr
D. Dalton
Answer: C
Explanation: Bohr introduced quantized energy levels.
39. Probability of finding an electron is maximum where
A. ψ = 0
B. ψ² is maximum
C. ψ is minimum
D. momentum is zero
Answer: B
Explanation: ψ² gives probability density.
40. Orbital differs from orbit because orbital
A. has fixed path
B. is circular
C. represents probability region
D. carries charge
Answer: C
Explanation: Orbitals show probability, not fixed paths.
41. Which quantum number has no negative value?
A. n
B. l
C. mₗ
D. s
Answer: A
Explanation: Principal quantum number is always positive.
42. The number of orbitals in n = 3 shell is
A. 3
B. 6
C. 9
D. 18
Answer: C
Explanation: Total orbitals = n² = 9.
43. Which orbital has lowest energy?
A. 2p
B. 3s
C. 1s
D. 2s
Answer: C
Explanation: Lower n value means lower energy.
44. Node is defined as region where
A. electron density is maximum
B. probability is zero
C. nucleus is present
D. energy is maximum
Answer: B
Explanation: Node has zero probability of electron presence.
45. The value of mₗ for s-orbital is
A. −1
B. 0
C. +1
D. −2
Answer: B
Explanation: s-orbital has only one orientation.
46. Which particle has no charge?
A. Proton
B. Electron
C. Neutron
D. Positron
Answer: C
Explanation: Neutron is electrically neutral.
47. Maximum electrons in M shell are
A. 8
B. 18
C. 32
D. 2
Answer: B
Explanation: Maximum electrons = 2n² = 18.
48. Which principle explains spectral lines?
A. Uncertainty principle
B. Aufbau principle
C. Bohr’s postulates
D. Hund’s rule
Answer: C
Explanation: Bohr explained line spectra.
49. The orbital with l = 2 is
A. s
B. p
C. d
D. f
Answer: C
Explanation: l = 2 corresponds to d-orbital.
50. Which statement is correct?
A. Orbitals are circular paths
B. Orbit and orbital are same
C. Orbitals have definite shape
D. Orbitals are flat
Answer: C
Explanation: Orbitals have definite shapes based on quantum numbers.
✅ Completion Note
This completes a fully NCERT-aligned, CBSE-standard set of 50 MCQs on Structure of Atom, covering all conceptual and numerical aspects required for Class 11 board exams.