1. Who is regarded as the “Father of Atomic Theory”?
A) J.J. Thomson
B) John Dalton
C) Ernest Rutherford
D) Niels Bohr
Answer: B
Explanation: John Dalton (1808) proposed the first modern atomic theory stating that matter is made up of indivisible particles called atoms.
2. The discovery of the electron is credited to:
A) Goldstein
B) J.J. Thomson
C) Rutherford
D) Bohr
Answer: B
Explanation: J.J. Thomson discovered the electron in 1897 using cathode ray tube experiments.
3. The charge of a proton is:
A) +1.6 × 10⁻¹⁹ C
B) –1.6 × 10⁻¹⁹ C
C) 0
D) 1 C
Answer: A
Explanation: A proton carries a positive elementary charge equal in magnitude to that of an electron but opposite in sign.
4. The neutron was discovered by:
A) Rutherford
B) Chadwick
C) Goldstein
D) Bohr
Answer: B
Explanation: James Chadwick discovered the neutron in 1932.
5. The smallest unit of an element which retains its identity is called:
A) Molecule
B) Atom
C) Ion
D) Proton
Answer: B
Explanation: An atom is the fundamental unit of matter that retains the chemical identity of the element.
6. Cathode rays are streams of:
A) Protons
B) Neutrons
C) Electrons
D) Alpha particles
Answer: C
Explanation: Cathode rays consist of negatively charged particles – electrons.
7. Which subatomic particle has the least mass?
A) Proton
B) Neutron
C) Electron
D) Positron
Answer: C
Explanation: The electron’s mass is about 1/1836 of a proton’s mass.
8. The nucleus of an atom consists of:
A) Only protons
B) Protons and neutrons
C) Only neutrons
D) Protons and electrons
Answer: B
Explanation: The atomic nucleus is made up of protons and neutrons, known as nucleons.
9. The positively charged rays in a discharge tube were discovered by:
A) Thomson
B) Rutherford
C) Goldstein
D) Chadwick
Answer: C
Explanation: Goldstein discovered canal rays (positive rays), later identified as protons.
10. The atomic number of an element represents:
A) Number of neutrons
B) Number of protons
C) Sum of protons and neutrons
D) Number of isotopes
Answer: B
Explanation: Atomic number (Z) = number of protons in the nucleus = number of electrons in a neutral atom.
11. Mass number (A) is equal to:
A) Protons only
B) Neutrons only
C) Protons + Neutrons
D) Protons + Electrons
Answer: C
Explanation: Mass number A = number of protons (Z) + number of neutrons (N).
12. Isotopes are atoms of the same element having:
A) Same atomic number, different mass number
B) Different atomic number, same mass number
C) Same number of neutrons
D) Different number of protons
Answer: A
Explanation: Isotopes differ in neutrons but have same protons.
13. Tritium is an isotope of hydrogen with:
A) 1 proton, 0 neutrons
B) 1 proton, 1 neutron
C) 1 proton, 2 neutrons
D) 2 protons, 1 neutron
Answer: C
Explanation: Tritium has 1 proton and 2 neutrons (mass number 3).
14. Which particle defines the chemical properties of an element?
A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: C
Explanation: Electrons, especially valence electrons, determine chemical behavior.
15. Which is heavier: neutron or proton?
A) Proton
B) Neutron
C) Both equal
D) Cannot say
Answer: B
Explanation: Neutron has a slightly greater mass than proton.
16. Which of the following is electrically neutral?
A) Proton
B) Neutron
C) Electron
D) Positron
Answer: B
Explanation: Neutrons carry no charge.
17. The electron was first named as “corpuscle” by:
A) Thomson
B) Rutherford
C) Bohr
D) Einstein
Answer: A
Explanation: J.J. Thomson called the electron a “corpuscle.”
18. The charge-to-mass ratio (e/m) of electron was determined by:
A) Rutherford
B) Millikan
C) Thomson
D) Bohr
Answer: C
Explanation: J.J. Thomson calculated the e/m ratio of electron in 1897.
19. The oil-drop experiment was performed by:
A) Rutherford
B) Millikan
C) Goldstein
D) Bohr
Answer: B
Explanation: R.A. Millikan measured the charge of the electron with the oil-drop experiment.
20. Which element has only one proton and no neutron?
A) Helium
B) Hydrogen-1
C) Deuterium
D) Tritium
Answer: B
Explanation: Protium (¹H) has 1 proton and 0 neutrons.
21. The concept of indivisible atoms was first given by:
A) Democritus
B) Dalton
C) Rutherford
D) Bohr
Answer: A
Explanation: Democritus (400 BC) coined the term “atomos” meaning indivisible.
22. Who discovered X-rays, which later helped in atomic studies?
A) Röntgen
B) Rutherford
C) Bohr
D) Chadwick
Answer: A
Explanation: Wilhelm Röntgen discovered X-rays in 1895.
23. The approximate radius of an atom is:
A) 10⁻¹⁰ m
B) 10⁻¹² m
C) 10⁻⁶ m
D) 1 m
Answer: A
Explanation: Atomic radius is about 1 Å = 10⁻¹⁰ m.
24. The radius of the nucleus is about:
A) 10⁻¹⁵ m
B) 10⁻¹⁰ m
C) 10⁻⁸ m
D) 10⁻³ m
Answer: A
Explanation: Nuclear radius is ~10⁻¹⁵ m (1 femtometer).
25. The concept of “plum pudding model” was given by:
A) Dalton
B) Thomson
C) Rutherford
D) Bohr
Answer: B
Explanation: J.J. Thomson proposed that electrons are embedded in a positively charged sphere (“plum pudding” model).
26. Rutherford’s alpha particle scattering experiment proved that:
A) Atoms are indivisible
B) Atoms have no charge
C) Atoms have a dense central nucleus
D) Electrons revolve in shells
Answer: C
Explanation: Rutherford’s experiment (1911) showed that most of the atom’s mass and positive charge is concentrated in a tiny nucleus.
27. In Rutherford’s experiment, most alpha particles passed through the gold foil without deflection. This showed that:
A) Atoms are hollow and empty
B) Atoms are solid spheres
C) Nucleus occupies whole atom
D) Electrons are inside nucleus
Answer: A
Explanation: Since most particles went undeflected, most of the atom is empty space.
28. According to Rutherford’s model, electrons:
A) Are stationary inside atom
B) Revolve around the nucleus
C) Are embedded in the nucleus
D) Do not exist
Answer: B
Explanation: Rutherford proposed that electrons revolve around nucleus like planets around the sun.
29. Major drawback of Rutherford’s model was:
A) Could not explain charge of nucleus
B) Could not explain stability of atom
C) Could not discover electron
D) Could not explain neutrons
Answer: B
Explanation: According to classical physics, orbiting electrons should radiate energy and fall into nucleus – instability problem.
30. Bohr introduced the concept of:
A) Stationary orbits
B) Neutrons
C) Atomic nucleus
D) Isotopes
Answer: A
Explanation: Bohr (1913) suggested electrons move in fixed orbits with quantized energy levels.
31. Bohr’s model successfully explained:
A) Spectrum of hydrogen atom
B) Spectrum of all heavy atoms
C) Discovery of neutrons
D) Alpha scattering
Answer: A
Explanation: Bohr’s model explains line spectra of hydrogen and hydrogen-like species.
32. In Bohr’s model, angular momentum of an electron is quantized and given by:
A) mvr = nh/2π
B) mvr = nh
C) mvr = h/2π
D) mvr = n²h
Answer: A
Explanation: Bohr’s postulate: angular momentum L = mvr = n(h/2π).
33. The energy of an electron in the nth orbit of hydrogen is proportional to:
A) +1/n²
B) –1/n²
C) +n²
D) –n
Answer: B
Explanation: Energy En = –13.6 eV/n² (negative sign shows bound state).
34. Which of the following transitions gives the Lyman series in hydrogen?
A) To n=2
B) To n=3
C) To n=1
D) To n=4
Answer: C
Explanation: Lyman series corresponds to electron transitions ending at n=1 (UV region).
35. The Balmer series of hydrogen lies in the:
A) Infrared region
B) Visible region
C) Ultraviolet region
D) X-ray region
Answer: B
Explanation: Balmer series (n→2) lies in visible region of electromagnetic spectrum.
36. The Paschen series lies in:
A) Visible region
B) UV region
C) Infrared region
D) Microwave region
Answer: C
Explanation: Paschen series corresponds to transitions to n=3 (infrared).
37. Rydberg’s constant for hydrogen is approximately:
A) 1.097 × 10⁷ m⁻¹
B) 6.022 × 10²³ mol⁻¹
C) 3 × 10⁸ m/s
D) 9.11 × 10⁻³¹ kg
Answer: A
Explanation: Rydberg constant R = 1.097 × 10⁷ m⁻¹, used for calculating spectral lines.
38. The principal quantum number (n) determines:
A) Shape of orbital
B) Orientation of orbital
C) Size and energy of orbital
D) Spin of electron
Answer: C
Explanation: Principal quantum number (n=1,2,3…) gives size and energy level of orbitals.
39. The azimuthal quantum number (l) determines:
A) Size of orbital
B) Shape of orbital
C) Energy of orbital only
D) Spin of orbital
Answer: B
Explanation: Azimuthal (angular momentum) quantum number l = 0,1,…,(n–1) gives orbital shape (s,p,d,f).
40. For l=2, the orbital is:
A) s-orbital
B) p-orbital
C) d-orbital
D) f-orbital
Answer: C
Explanation: l=0 → s, l=1 → p, l=2 → d, l=3 → f.
41. The magnetic quantum number (m) determines:
A) Energy level
B) Shape of orbital
C) Orientation of orbital
D) Spin of orbital
Answer: C
Explanation: m ranges from –l to +l, describing orientation of orbitals in space.
42. For l=1, possible values of m are:
A) 0
B) –1, 0, +1
C) –2, –1, 0, +1, +2
D) +1 only
Answer: B
Explanation: For l=1, m = –1,0,+1 → three p-orbitals (px, py, pz).
43. The spin quantum number (s) has values:
A) 0 and 1
B) +½ and –½
C) –1 and +1
D) –2 and +2
Answer: B
Explanation: Spin quantum number ms = +½ (spin up), –½ (spin down).
44. Maximum number of electrons in an orbital is:
A) 1
B) 2
C) 3
D) 4
Answer: B
Explanation: Each orbital can hold maximum 2 electrons with opposite spins (Pauli principle).
45. The maximum number of electrons in a shell with principal quantum number n is:
A) 2n
B) 2n²
C) n²
D) n³
Answer: B
Explanation: Each shell can hold maximum 2n² electrons.
46. The 3rd shell (n=3) can hold a maximum of:
A) 8 electrons
B) 18 electrons
C) 32 electrons
D) 50 electrons
Answer: B
Explanation: Maximum electrons in n=3 → 2n² = 2×9 = 18.
47. The number of orbitals in a subshell with quantum number l is:
A) 2l+1
B) 2n²
C) n²
D) 2n+1
Answer: A
Explanation: Number of orbitals in subshell = 2l+1.
48. How many orbitals are possible in the d-subshell?
A) 3
B) 5
C) 7
D) 9
Answer: B
Explanation: For l=2 (d), number of orbitals = 2l+1 = 5.
49. Maximum electrons in f-subshell is:
A) 7
B) 14
C) 10
D) 18
Answer: B
Explanation: f-subshell has 7 orbitals → max 14 electrons.
50. If n=4, l=2, number of orbitals possible is:
A) 3
B) 5
C) 7
D) 9
Answer: B
Explanation: For l=2, orbitals = 2l+1 = 5 (d-orbitals in 4th shell).
51. The arrangement of electrons in shells and subshells of an atom is called:
A) Atomic structure
B) Electronic configuration
C) Isotopy
D) Valency
Answer: B
Explanation: The distribution of electrons among orbitals of an atom is called electronic configuration.
52. Which principle states that no two electrons in an atom can have all four quantum numbers identical?
A) Hund’s rule
B) Pauli exclusion principle
C) Aufbau principle
D) Heisenberg principle
Answer: B
Explanation: Pauli exclusion principle states that each orbital can hold maximum 2 electrons with opposite spins.
53. Aufbau principle is concerned with:
A) Stability of nucleus
B) Order of filling orbitals
C) Shape of orbitals
D) Orientation of orbitals
Answer: B
Explanation: Aufbau principle explains the sequence in which orbitals are filled with electrons (lowest energy first).
54. According to Aufbau principle, which orbital fills after 3p?
A) 3d
B) 4s
C) 4p
D) 4f
Answer: B
Explanation: Order of filling: 1s → 2s → 2p → 3s → 3p → 4s → 3d …
55. Which rule states that electrons occupy orbitals singly first before pairing?
A) Pauli exclusion principle
B) Hund’s rule of maximum multiplicity
C) Aufbau principle
D) Octet rule
Answer: B
Explanation: Hund’s rule: In degenerate orbitals, electrons fill singly with parallel spins before pairing.
56. The ground-state electronic configuration of oxygen (Z=8) is:
A) 1s² 2s² 2p⁶
B) 1s² 2s² 2p⁴
C) 1s² 2s¹ 2p⁵
D) 1s² 2s² 2p³
Answer: B
Explanation: Oxygen has 8 electrons: 1s² 2s² 2p⁴.
57. The electronic configuration of sodium (Z=11) is:
A) 1s² 2s² 2p⁶ 3s¹
B) 1s² 2s² 2p⁵ 3s²
C) 1s² 2s² 2p⁶
D) 1s² 2s² 2p³
Answer: A
Explanation: Sodium: 1s² 2s² 2p⁶ 3s¹ (outermost electron in 3s).
58. Which element has configuration [He]2s²2p²?
A) Beryllium
B) Boron
C) Carbon
D) Nitrogen
Answer: C
Explanation: Carbon (Z=6) has 1s²2s²2p².
59. Which element has a half-filled p-subshell?
A) Boron (Z=5)
B) Nitrogen (Z=7)
C) Oxygen (Z=8)
D) Fluorine (Z=9)
Answer: B
Explanation: Nitrogen: 1s² 2s² 2p³ → half-filled 2p subshell.
60. The configuration of chlorine (Z=17) is:
A) 1s² 2s² 2p⁶ 3s² 3p⁵
B) 1s² 2s² 2p⁶ 3s² 3p⁶
C) 1s² 2s² 2p⁶ 3s² 3p⁴
D) 1s² 2s² 2p⁵ 3s² 3p⁶
Answer: A
Explanation: Chlorine has 17 electrons → 1s² 2s² 2p⁶ 3s² 3p⁵.
61. The general electronic configuration of alkali metals is:
A) ns¹
B) ns²
C) ns² np⁶
D) ns² np¹
Answer: A
Explanation: Alkali metals have one electron in outermost s-orbital (ns¹).
62. Which of the following has an outer electronic configuration of ns² np⁵?
A) Alkali metals
B) Alkaline earth metals
C) Halogens
D) Noble gases
Answer: C
Explanation: Halogens have 7 valence electrons (ns²np⁵).
63. Noble gases have the general configuration:
A) ns² np¹
B) ns² np⁵
C) ns² np⁶
D) ns² np³
Answer: C
Explanation: Noble gases have complete octets → ns² np⁶ (except helium: 1s²).
64. The electronic configuration of calcium (Z=20) is:
A) [Ar]4s²
B) [Ne]3s² 3p⁶ 3d²
C) [Ar]3d²
D) [Ne]3s² 3p⁵
Answer: A
Explanation: Calcium: 1s²2s²2p⁶3s²3p⁶4s² → [Ar]4s².
65. Which has an anomalous configuration due to half-filled stability?
A) Zn (Z=30)
B) Cr (Z=24)
C) Ca (Z=20)
D) Ne (Z=10)
Answer: B
Explanation: Chromium: [Ar]3d⁵4s¹ instead of [Ar]3d⁴4s² (extra stability of half-filled 3d).
66. Copper (Z=29) has electronic configuration:
A) [Ar]3d⁹4s²
B) [Ar]3d¹⁰4s¹
C) [Ar]3d¹⁰4s²
D) [Ar]3d⁸4s²
Answer: B
Explanation: Copper: [Ar]3d¹⁰4s¹ (due to stability of fully-filled d-orbital).
67. The maximum number of electrons that can be filled in 3d subshell is:
A) 8
B) 10
C) 12
D) 14
Answer: B
Explanation: d-subshell has 5 orbitals, each holds 2 electrons → max 10.
68. Which orbital will be filled first according to Aufbau rule?
A) 4s
B) 3d
C) 4p
D) 5s
Answer: A
Explanation: 4s has lower energy than 3d, so it fills first.
69. Which among the following represents the correct order of filling of orbitals?
A) 3p → 3d → 4s
B) 3p → 4s → 3d
C) 4s → 3p → 3d
D) 3d → 3p → 4s
Answer: B
Explanation: Correct order: 3p → 4s → 3d (Aufbau principle).
70. According to Pauli exclusion principle, the two electrons in the same orbital differ in:
A) n
B) l
C) m
D) s (spin quantum number)
Answer: D
Explanation: Two electrons in same orbital must have opposite spins.
71. Which of the following orbitals will have the lowest energy?
A) 3d
B) 4s
C) 4p
D) 5s
Answer: B
Explanation: 4s has slightly lower energy than 3d (exceptions exist for transition metals).
72. The configuration of Fe (Z=26) is:
A) [Ar]3d⁴4s²
B) [Ar]3d⁶4s²
C) [Ar]3d⁵4s¹
D) [Ar]3d⁷4s¹
Answer: B
Explanation: Iron: 1s²2s²2p⁶3s²3p⁶3d⁶4s² → [Ar]3d⁶4s².
73. Which element has completely filled d-subshell in its ground state?
A) Sc (Z=21)
B) Zn (Z=30)
C) Cr (Z=24)
D) Cu (Z=29)
Answer: B
Explanation: Zn: [Ar]3d¹⁰4s² → fully filled d-orbital.
74. The number of unpaired electrons in nitrogen (Z=7) is:
A) 1
B) 2
C) 3
D) 4
Answer: C
Explanation: N: 1s²2s²2p³ → three unpaired electrons in 2p orbitals.
75. Which of the following elements has a stable octet configuration in its ground state?
A) Oxygen
B) Neon
C) Sodium
D) Chlorine
Answer: B
Explanation: Neon (Z=10) has a full octet (1s²2s²2p⁶). Hence chemically inert.
76. Which scientist proposed the wave nature of electrons?
A) Bohr
B) Heisenberg
C) de Broglie
D) Planck
Answer: C
Explanation: Louis de Broglie (1924) proposed electrons behave like waves with wavelength λ = h/p.
77. The de Broglie wavelength of a particle is given by:
A) λ = h/mv
B) λ = mv/h
C) λ = hν
D) λ = c/ν
Answer: A
Explanation: De Broglie wavelength λ = h/p = h/(mv).
78. The uncertainty principle was given by:
A) Planck
B) Bohr
C) Heisenberg
D) Schrödinger
Answer: C
Explanation: Heisenberg’s Uncertainty Principle: Δx·Δp ≥ h/4π.
79. The uncertainty principle is significant only for:
A) Macroscopic objects
B) Microscopic particles like electrons
C) Planets
D) Satellites
Answer: B
Explanation: Uncertainty is negligible for large bodies but important for atomic particles.
80. Schrödinger equation deals with:
A) Particle nature of electron
B) Wave nature of electron
C) Nuclear reactions
D) Spectroscopy of atoms
Answer: B
Explanation: Schrödinger wave equation describes the wave behavior of electrons in atoms.
81. Quantum mechanical model of the atom was developed by:
A) Bohr
B) Schrödinger
C) Rutherford
D) Thomson
Answer: B
Explanation: Schrödinger’s model is the most accepted atomic model.
82. Atomic orbital is defined as:
A) Definite path of electron
B) Region of space where probability of finding electron is maximum
C) Location of protons
D) Path of nucleus
Answer: B
Explanation: Orbital is a 3D region of maximum electron probability (90%).
83. The s-orbital is:
A) Dumbbell shaped
B) Spherical
C) Double dumbbell
D) Complex shape
Answer: B
Explanation: s-orbitals are spherical in shape.
84. The p-orbitals are:
A) Spherical
B) Dumbbell shaped
C) Double dumbbell
D) Spherical with nodes
Answer: B
Explanation: p-orbitals (px, py, pz) are dumbbell-shaped.
85. The d-orbitals are:
A) Dumbbell shaped
B) Spherical
C) Double dumbbell/complex
D) Circular
Answer: C
Explanation: d-orbitals have double dumbbell or cloverleaf shapes.
86. Number of nodal planes in p-orbital is:
A) 0
B) 1
C) 2
D) 3
Answer: B
Explanation: p-orbital has one nodal plane passing through nucleus.
87. The number of radial nodes in an orbital is given by:
A) n–l–1
B) n+l
C) 2l+1
D) l–1
Answer: A
Explanation: Radial nodes = n – l – 1.
88. The number of angular nodes is equal to:
A) n–l–1
B) l
C) n²
D) 2l+1
Answer: B
Explanation: Angular nodes depend on azimuthal quantum number (l).
89. The total number of nodes in an orbital is:
A) n–1
B) n²
C) 2n
D) l–1
Answer: A
Explanation: Total nodes = n – 1 = (radial + angular).
90. Which orbital has no nodes?
A) 1s
B) 2s
C) 2p
D) 3p
Answer: A
Explanation: 1s orbital has n=1, total nodes = 0.
91. Which orbital has spherical symmetry?
A) p
B) d
C) f
D) s
Answer: D
Explanation: s-orbitals are spherically symmetric around the nucleus.
92. Maximum number of electrons in 4f-subshell is:
A) 7
B) 10
C) 14
D) 18
Answer: C
Explanation: f-subshell has 7 orbitals → max 14 electrons.
93. Degenerate orbitals are orbitals having:
A) Same shape
B) Same energy
C) Same nucleus
D) Same orientation
Answer: B
Explanation: Orbitals with same energy are called degenerate (e.g., px, py, pz).
94. Which of the following orbitals does not exist?
A) 1p
B) 2p
C) 3d
D) 4f
Answer: A
Explanation: For n=1, l=0 only (s-orbital). 1p does not exist.
95. Which set of quantum numbers is not possible?
A) n=3, l=2, m=0, s=+½
B) n=2, l=1, m=+1, s=–½
C) n=1, l=0, m=0, s=+½
D) n=3, l=3, m=0, s=+½
Answer: D
Explanation: For n=3, maximum l = n–1 = 2. So l=3 is not possible.
96. Which scientist proposed the dual nature of radiation?
A) Einstein
B) Planck
C) Bohr
D) de Broglie
Answer: B
Explanation: Max Planck proposed quantum theory of radiation (1900), Einstein later explained photoelectric effect (1905).
97. Einstein explained the photoelectric effect using the concept of:
A) Wave theory
B) Particle (photon) nature of light
C) String theory
D) Quantum mechanical model
Answer: B
Explanation: Einstein used photon theory: light is made of discrete packets (photons).
98. The energy of a photon is given by:
A) E = h/λ
B) E = hν
C) E = mc²
D) E = h²/2m
Answer: B
Explanation: Energy of photon = hν = hc/λ.
99. The frequency of a photon with wavelength 600 nm is approximately:
A) 3 × 10¹⁵ Hz
B) 5 × 10¹⁴ Hz
C) 6 × 10¹² Hz
D) 5 × 10¹⁶ Hz
Answer: B
Explanation: ν = c/λ = 3×10⁸ / 600×10⁻⁹ ≈ 5×10¹⁴ Hz.
100. Which atomic model is the most widely accepted today?
A) Rutherford model
B) Bohr model
C) Quantum mechanical model
D) Plum pudding model
Answer: C
Explanation: The quantum mechanical model (Schrödinger’s model) is the modern accepted model of the atom.