Structure of Atom Practice

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NEET Chemistry - Chapter 2

Structure of Atom Practice Tests

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Basic particles
1. The particle carrying a positive charge in the atom is:
- A. Proton (Correct)
- B. Electron
- C. Neutron
- D. Photon
Explanation: Protons are positively charged and present in the nucleus.
Basic particles
2. Atomic number represents the number of:
- A. Protons (Correct)
- B. Neutrons
- C. Nucleons
- D. Electrons plus neutrons
Explanation: Atomic number uniquely identifies the element.
Basic particles
3. Mass number is equal to:
- A. Protons + neutrons (Correct)
- B. Only neutrons
- C. Only electrons
- D. Protons - neutrons
Explanation: It counts total nucleons in the nucleus.
Subatomic relation
4. In a neutral atom, number of electrons equals:
- A. Number of protons (Correct)
- B. Number of neutrons
- C. Mass number
- D. Twice atomic number
Explanation: Neutrality requires total positive and negative charges to match.
Cathode rays
5. Cathode rays are streams of:
- A. Electrons (Correct)
- B. Protons
- C. Neutrons
- D. Alpha particles
Explanation: J.J. Thomson established the electron through cathode ray experiments.
Anode rays
6. Canal rays mainly helped in the discovery of:
- A. Proton-like positive particles (Correct)
- B. Neutrons
- C. Photons
- D. X-rays
Explanation: Positive rays pointed to positively charged subatomic particles.
Thomson model
7. In Thomson's atomic model, electrons were embedded in a sphere of:
- A. Positive charge (Correct)
- B. Negative charge
- C. Neutrons
- D. Vacuum
Explanation: It is the 'plum pudding' model.
Rutherford experiment
8. Most alpha particles passed undeviated through gold foil because atoms are mostly:
- A. Empty space (Correct)
- B. Solid spheres
- C. Filled with electrons
- D. Filled with neutrons
Explanation: Rutherford concluded most atomic volume is empty.
Rutherford experiment
9. The dense central core of the atom was called:
- A. Nucleus (Correct)
- B. Orbit
- C. Shell
- D. Cloud
Explanation: Rutherford proposed a small dense positively charged nucleus.
Rutherford model
10. Rutherford's model could not explain:
- A. Atomic stability (Correct)
- B. Existence of nucleus
- C. Positive charge in nucleus
- D. Scattering of alpha particles
Explanation: Classical electrodynamics predicted orbiting electrons would lose energy.
Electromagnetic radiation
11. Speed of electromagnetic radiation in vacuum is:
- A. $3\times10^8$ m s$^{-1}$ (Correct)
- B. $3\times10^6$ m s$^{-1}$
- C. $3\times10^{10}$ m s$^{-1}$
- D. $1.5\times10^8$ m s$^{-1}$
Explanation: That is the speed of light in vacuum.
Radiation relation
12. The relation between wavelength and frequency is:
- A. $c=\lambda\nu$ (Correct)
- B. $c=\lambda/\nu$
- C. $c=\nu/\lambda$
- D. $c=\lambda+\nu$
Explanation: Wave speed equals wavelength times frequency.
Planck theory
13. Energy of a photon is:
- A. $E=h\nu$ (Correct)
- B. $E=mc^2$
- C. $E=RT$
- D. $E=\lambda/h$
Explanation: Planck related energy to frequency using Planck constant.
Photoelectric effect
14. Photoelectric effect supports the particle nature of light because it shows:
- A. Light transfers energy in discrete quanta (Correct)
- B. Light is only a wave
- C. Electrons have no mass
- D. Nucleus is unstable
Explanation: Emission occurs only when photons have sufficient threshold energy.
Bohr idea
15. Bohr proposed that electrons revolve only in:
- A. Certain permitted stationary orbits (Correct)
- B. Any orbit with any radius
- C. Elliptical paths only
- D. Random clouds
Explanation: Only selected orbits were allowed without energy loss.
Bohr idea
16. Angular momentum of electron in Bohr orbit is quantized as:
- A. $mvr=\dfrac{nh}{2\pi}$ (Correct)
- B. $mvr=nh$
- C. $mvr=2nh$
- D. $mvr=\dfrac{h}{n}$
Explanation: This is Bohr's quantization condition.
Hydrogen spectrum
17. Bohr model successfully explained the spectrum of:
- A. Hydrogen atom (Correct)
- B. All multi-electron atoms equally well
- C. Nucleus only
- D. Compounds
Explanation: It worked best for one-electron species.
Atomic species
18. Which is a one-electron species?
- A. $He^+$ (Correct)
- B. He
- C. Li
- D. Be
Explanation: Singly ionised helium has only one electron.
Atomic species
19. Bohr model is applicable to:
- A. Hydrogen-like species (Correct)
- B. All molecules
- C. Only neutral atoms
- D. Only noble gases
Explanation: Any one-electron species can be treated similarly.
Chapter logic
20. The main limitation of Rutherford model was that it did not address:
- A. Why orbiting electrons do not collapse into nucleus (Correct)
- B. Presence of positive charge
- C. Existence of alpha particles
- D. Scattering apparatus
Explanation: The model lacked a stability mechanism.
Spectrum
21. Line spectra arise because atomic energies are:
- A. Quantized (Correct)
- B. Continuous
- C. Unstable only
- D. Equal for all atoms
Explanation: Only specific transitions are allowed.
Photon logic
22. Higher frequency radiation has:
- A. Higher energy per photon (Correct)
- B. Lower energy per photon
- C. Same photon energy
- D. Zero wavelength
Explanation: $E=h\nu$, so energy increases with frequency.
Wavelength logic
23. Shorter wavelength corresponds to:
- A. Higher frequency (Correct)
- B. Lower frequency
- C. Lower speed in vacuum
- D. No radiation
Explanation: Since $c$ is constant, smaller wavelength means larger frequency.
Nuclear dimensions
24. The nucleus occupies only a very small fraction of atomic volume, so the atom is considered:
- A. Mostly empty (Correct)
- B. Mostly solid
- C. Completely continuous
- D. Made only of waves
Explanation: That was the key Rutherford conclusion.
Chapter logic
25. The historical sequence best supported by experiments is:
- A. Thomson model, Rutherford model, Bohr model (Correct)
- B. Bohr model, Thomson model, Rutherford model
- C. Rutherford model, Bohr model, Thomson model
- D. Bohr model, Rutherford model, Thomson model
Explanation: Atomic models evolved with new experimental evidence.
Bohr radius
26. The radius of the first Bohr orbit of hydrogen is denoted by:
- A. $a_0$ (Correct)
- B. $r_0$
- C. $h$
- D. $\lambda_0$
Explanation: $a_0$ is the Bohr radius.
Bohr radius
27. Radius of nth orbit in hydrogen-like species varies as:
- A. $n^2/Z$ (Correct)
- B. $n/Z^2$
- C. $Z/n^2$
- D. $1/n$
Explanation: Bohr radius formula scales this way.
Energy level
28. Energy of nth orbit in hydrogen is proportional to:
- A. $-1/n^2$ (Correct)
- B. $-n^2$
- C. $1/n$
- D. Constant
Explanation: Bohr energies become less negative with increasing n.
Energy level
29. Ground state of hydrogen corresponds to:
- A. n = 1 (Correct)
- B. n = 2
- C. n = 0
- D. n = infinity
Explanation: The lowest allowed orbit is the ground state.
Excited state
30. Any state with n greater than 1 is called:
- A. Excited state (Correct)
- B. Ground state
- C. Forbidden state
- D. Valence state
Explanation: Its energy is higher than the ground state.
Transition
31. When an electron jumps from higher to lower orbit, it:
- A. Emits energy (Correct)
- B. Absorbs energy
- C. Loses charge
- D. Changes proton number
Explanation: Downward transition releases a photon.
Transition
32. When an electron jumps from lower to higher orbit, it:
- A. Absorbs energy (Correct)
- B. Emits energy
- C. Becomes a proton
- D. Stops moving
Explanation: Energy must be supplied for excitation.
Ionisation energy
33. Ionisation energy of hydrogen from ground state is:
- A. 13.6 eV (Correct)
- B. 3.4 eV
- C. 10.2 eV
- D. 27.2 eV
Explanation: Removing the electron from n = 1 to n = infinity needs 13.6 eV.
Excitation energy
34. Energy required to excite hydrogen from n = 1 to n = 2 is:
- A. 10.2 eV (Correct)
- B. 13.6 eV
- C. 3.4 eV
- D. 1.89 eV
Explanation: Difference between -13.6 eV and -3.4 eV is 10.2 eV.
Spectral series
35. The Lyman series lies in the:
- A. Ultraviolet region (Correct)
- B. Visible region
- C. Infrared region
- D. Microwave region
Explanation: These transitions end at n = 1.
Spectral series
36. The Balmer series lies in the:
- A. Visible region (Correct)
- B. Ultraviolet region
- C. X-ray region
- D. Radio region
Explanation: Balmer lines correspond to transitions ending at n = 2.
Spectral series
37. Paschen series corresponds to transitions ending at:
- A. n = 3 (Correct)
- B. n = 1
- C. n = 2
- D. n = 4
Explanation: Paschen lines lie in the infrared region.
Spectral series
38. The Rydberg equation is used to calculate:
- A. Wavelength of spectral lines (Correct)
- B. Mass of electron
- C. Charge on proton
- D. Neutron number
Explanation: It predicts hydrogen spectral wavelengths.
Hydrogen-like ions
39. For $He^+$, the energy of first orbit is:
- A. -54.4 eV (Correct)
- B. -13.6 eV
- C. -27.2 eV
- D. -3.4 eV
Explanation: Energy scales as $-13.6Z^2/n^2$ and here Z = 2.
Hydrogen-like ions
40. Ionisation energy of $Li^{2+}$ from ground state is:
- A. 122.4 eV (Correct)
- B. 13.6 eV
- C. 40.8 eV
- D. 81.6 eV
Explanation: For Z = 3, ionisation energy is 13.6 × 9.
Wavelength relation
41. Maximum wavelength in Balmer series corresponds to transition:
- A. 3 to 2 (Correct)
- B. 4 to 2
- C. infinity to 2
- D. 2 to 1
Explanation: Smallest energy gap in a series gives the longest wavelength.
Wavelength relation
42. Minimum wavelength in Lyman series corresponds to transition:
- A. infinity to 1 (Correct)
- B. 2 to 1
- C. 3 to 1
- D. 4 to 1
Explanation: Largest energy drop in the series gives shortest wavelength.
Orbit property
43. As n increases in hydrogen atom, orbit radius:
- A. Increases (Correct)
- B. Decreases
- C. Remains same
- D. Becomes zero
Explanation: Radius varies as $n^2$.
Orbit property
44. As n increases, electron energy becomes:
- A. Less negative (Correct)
- B. More negative
- C. Zero immediately
- D. Unchanged
Explanation: The electron moves toward ionisation with increasing n.
Velocity relation
45. Electron velocity in Bohr model varies with:
- A. $Z/n$ (Correct)
- B. $n/Z$
- C. $n^2/Z$
- D. $Z^2/n$
Explanation: Velocity decreases with higher n and increases with nuclear charge.
Line spectrum
46. Emission spectrum is produced when electrons:
- A. Fall from higher to lower levels (Correct)
- B. Move from lower to higher levels only
- C. Are removed completely
- D. Remain in same orbit
Explanation: These transitions emit photons of specific wavelengths.
Absorption
47. Absorption lines arise when atoms:
- A. Absorb certain wavelengths for upward transition (Correct)
- B. Emit all wavelengths
- C. Scatter only electrons
- D. Lose protons
Explanation: Only energies matching allowed gaps are absorbed.
Series logic
48. Which series has the lowest-energy photons?
- A. Paschen (Correct)
- B. Lyman
- C. Balmer
- D. Brackett has lower than Paschen, but among these Paschen
Explanation: Transitions ending at n = 3 involve smaller energy gaps than Lyman or Balmer.
NEET trap
49. In Bohr model, angular momentum is quantized, so allowed electron paths are:
- A. Discrete, not continuous (Correct)
- B. Continuous circles of any radius
- C. Randomly oriented only
- D. Independent of n
Explanation: Only selected states satisfy the quantization condition.
Chapter logic
50. The Bohr model's biggest success was explaining:
- A. Hydrogen spectral frequencies quantitatively (Correct)
- B. Chemical bonding in all molecules
- C. Electron spin
- D. Shape of p orbitals
Explanation: It correctly predicted line energies for one-electron atoms.
de Broglie
51. de Broglie proposed that moving particles have associated:
- A. Wave character (Correct)
- B. Only charge
- C. Only mass
- D. Only magnetic field
Explanation: Matter waves were proposed for particles in motion.
de Broglie
52. The de Broglie wavelength is:
- A. $\lambda=h/mv$ (Correct)
- B. $\lambda=mv/h$
- C. $\lambda=h\nu$
- D. $\lambda=mc^2$
Explanation: Momentum and wavelength are inversely related.
de Broglie
53. A particle with larger momentum has:
- A. Shorter wavelength (Correct)
- B. Longer wavelength
- C. Same wavelength
- D. Zero wavelength
Explanation: Since $\lambda=h/p$, wavelength decreases as momentum rises.
Heisenberg principle
54. It is impossible to determine simultaneously the exact position and exact:
- A. Momentum of a particle (Correct)
- B. Mass of a particle
- C. Charge of a particle
- D. Spin of a particle
Explanation: This is Heisenberg's uncertainty principle.
Heisenberg principle
55. Uncertainty principle mainly becomes important for:
- A. Microscopic particles (Correct)
- B. Planets
- C. Cars
- D. Macroscopic balls
Explanation: Quantum effects matter at very small scales.
Wave mechanics
56. Schrodinger's equation gives information about:
- A. Wave function and allowed energies (Correct)
- B. Exact electron path
- C. Proton number
- D. Nuclear size directly
Explanation: It forms the basis of quantum mechanical model.
Wave function
57. The square of wave function gives:
- A. Probability density (Correct)
- B. Electron charge
- C. Mass number
- D. Spin value
Explanation: $\psi^2$ gives the likelihood of finding the electron.
Orbitals
58. An orbital is a region in space where the probability of finding an electron is:
- A. Maximum (Correct)
- B. Zero always
- C. Exactly fixed at one point
- D. Independent of energy
Explanation: It replaces the old fixed-orbit picture.
Quantum numbers
59. The principal quantum number is represented by:
- A. n (Correct)
- B. l
- C. m
- D. s
Explanation: It largely decides size and energy level.
Quantum numbers
60. The azimuthal quantum number is represented by:
- A. l (Correct)
- B. n
- C. m
- D. s
Explanation: It determines subshell and orbital shape.
Quantum numbers
61. The magnetic quantum number is represented by:
- A. m (Correct)
- B. n
- C. l
- D. s
Explanation: It indicates orientation of orbital.
Quantum numbers
62. Spin quantum number can have values:
- A. $+1/2$ and $-1/2$ (Correct)
- B. 0 and 1
- C. 1 and 2
- D. $+1$ and $-1$
Explanation: Electron spin has two allowed orientations.
Subshell count
63. For n = 3, the allowed values of l are:
- A. 0, 1, 2 (Correct)
- B. 0, 1
- C. 1, 2, 3
- D. 0, 1, 2, 3
Explanation: l ranges from 0 to n - 1.
Orbital count
64. Number of orbitals in a subshell is:
- A. $2l+1$ (Correct)
- B. $n^2$
- C. $2n^2$
- D. $l^2$
Explanation: Each subshell contains these many orbitals.
Orbital count
65. Number of orbitals in p-subshell is:
- A. 3 (Correct)
- B. 1
- C. 5
- D. 7
Explanation: For p, l = 1, so 2l+1 = 3.
Orbital count
66. Number of orbitals in d-subshell is:
- A. 5 (Correct)
- B. 3
- C. 7
- D. 1
Explanation: For d, l = 2, so there are 5 orbitals.
Electron capacity
67. Maximum number of electrons in an orbital is:
- A. 2 (Correct)
- B. 1
- C. 4
- D. 6
Explanation: Pauli exclusion principle allows at most two with opposite spins.
Electron capacity
68. Maximum number of electrons in p-subshell is:
- A. 6 (Correct)
- B. 2
- C. 10
- D. 14
Explanation: Three p orbitals hold 6 electrons.
Electron capacity
69. Maximum number of electrons in n = 3 shell is:
- A. 18 (Correct)
- B. 8
- C. 32
- D. 9
Explanation: Shell capacity is $2n^2$.
Shapes
70. s-orbitals are generally:
- A. Spherical (Correct)
- B. Dumb-bell shaped
- C. Clover-leaf shaped
- D. Planar triangles
Explanation: s-orbitals are spherically symmetric.
Shapes
71. p-orbitals are generally:
- A. Dumb-bell shaped (Correct)
- B. Spherical
- C. Ring shaped
- D. Tetrahedral
Explanation: Each p orbital has two lobes.
Nodes
72. Total number of nodes in an orbital is:
- A. n - 1 (Correct)
- B. n
- C. l
- D. 2n - 1
Explanation: Total nodes are sum of radial and angular nodes.
Angular nodes
73. Number of angular nodes equals:
- A. l (Correct)
- B. n - l - 1
- C. n - 1
- D. 2l + 1
Explanation: Angular node count depends only on azimuthal quantum number.
Radial nodes
74. Number of radial nodes equals:
- A. n - l - 1 (Correct)
- B. n - 1
- C. l
- D. 2n
Explanation: This is the standard formula.
Chapter logic
75. Quantum mechanics replaced fixed Bohr orbits with:
- A. Probability-based orbitals described by wave functions (Correct)
- B. Exact circular paths of variable width
- C. A solid electron shell
- D. Classical planetary paths
Explanation: Electron location is treated probabilistically, not as a fixed path.
Aufbau principle
76. Electrons fill orbitals in order of:
- A. Increasing energy (Correct)
- B. Increasing spin only
- C. Alphabetical order
- D. Random arrangement
Explanation: Lower-energy orbitals are filled first.
n+l rule
77. According to n+l rule, lower value of n+l means:
- A. Lower energy orbital (Correct)
- B. Higher energy orbital
- C. More electrons always
- D. Smaller atom always
Explanation: This rule is used to predict filling order.
n+l rule
78. Between 4s and 3d, the lower energy orbital during filling is:
- A. 4s (Correct)
- B. 3d
- C. Both equal
- D. Depends only on element
Explanation: Because 4s has lower n+l value than 3d.
Pauli principle
79. No two electrons in an atom can have the same set of:
- A. Four quantum numbers (Correct)
- B. Principal quantum number only
- C. Spin quantum number only
- D. Azimuthal quantum number only
Explanation: This is Pauli exclusion principle.
Hund rule
80. Hund's rule says electrons in degenerate orbitals occupy them:
- A. Singly first with parallel spins (Correct)
- B. Pair first with opposite spins
- C. Randomly
- D. Only after full shell
Explanation: This maximizes multiplicity and lowers repulsion.
Electronic configuration
81. Electronic configuration of oxygen (Z = 8) is:
- A. $1s^22s^22p^4$ (Correct)
- B. $1s^22s^22p^6$
- C. $1s^22s^23s^4$
- D. $1s^22p^6$
Explanation: Eight electrons fill in this order.
Electronic configuration
82. Electronic configuration of sodium (Z = 11) is:
- A. $1s^22s^22p^63s^1$ (Correct)
- B. $1s^22s^22p^53s^2$
- C. $1s^22s^22p^63p^1$
- D. $1s^22s^22p^64s^1$
Explanation: The eleventh electron enters 3s.
Electronic configuration
83. Electronic configuration of chromium is exceptional because it is:
- A. $[Ar]3d^54s^1$ (Correct)
- B. $[Ar]3d^44s^2$
- C. $[Ar]3d^64s^0$
- D. $[Ar]3d^34s^3$
Explanation: Half-filled d-subshell offers extra stability.
Electronic configuration
84. Electronic configuration of copper is exceptional because it is:
- A. $[Ar]3d^{10}4s^1$ (Correct)
- B. $[Ar]3d^94s^2$
- C. $[Ar]3d^84s^3$
- D. $[Ar]3d^{10}4s^2$
Explanation: Completely filled d-subshell gives additional stability.
Valence shell
85. Valence electrons are electrons in the:
- A. Outermost shell (Correct)
- B. Innermost shell
- C. Nucleus
- D. All orbitals equally
Explanation: They largely determine chemical behavior.
Orbital filling
86. Nitrogen (Z = 7) has number of unpaired electrons equal to:
- A. 3 (Correct)
- B. 1
- C. 2
- D. 0
Explanation: Configuration $1s^22s^22p^3$ places one electron in each p orbital.
Orbital filling
87. Oxygen (Z = 8) has number of unpaired electrons equal to:
- A. 2 (Correct)
- B. 1
- C. 3
- D. 0
Explanation: In $2p^4$, one pair forms and two electrons remain unpaired.
Orbital filling
88. The number of unpaired electrons in $Fe^{3+}$ is:
- A. 5 (Correct)
- B. 3
- C. 4
- D. 1
Explanation: Fe is [Ar]3d$^6$4s$^2$; Fe$^{3+}$ becomes [Ar]3d$^5$.
Orbital filling
89. The number of unpaired electrons in $Cu^{2+}$ is:
- A. 1 (Correct)
- B. 0
- C. 2
- D. 9
Explanation: Cu is [Ar]3d$^{10}$4s$^1$; Cu$^{2+}$ becomes [Ar]3d$^9$.
Magnetic nature
90. A species with one or more unpaired electrons is:
- A. Paramagnetic (Correct)
- B. Diamagnetic
- C. Isotopic
- D. Isoelectronic
Explanation: Unpaired electrons cause attraction in a magnetic field.
Magnetic nature
91. A species with all electrons paired is:
- A. Diamagnetic (Correct)
- B. Paramagnetic
- C. Ferromagnetic only
- D. Electropositive
Explanation: All paired electrons cancel magnetic moments.
Quantum number set
92. For a 3p electron, n and l are respectively:
- A. 3 and 1 (Correct)
- B. 1 and 3
- C. 3 and 2
- D. 2 and 1
Explanation: p-subshell corresponds to l = 1.
Quantum number set
93. For a 4d electron, allowed m values are:
- A. -2, -1, 0, +1, +2 (Correct)
- B. -1, 0, +1
- C. 0 only
- D. -3 to +3
Explanation: For d, l = 2 and m ranges from -l to +l.
Capacity
94. Maximum number of electrons in 4th shell is:
- A. 32 (Correct)
- B. 18
- C. 16
- D. 8
Explanation: Use $2n^2$ with n = 4.
Capacity
95. Maximum number of electrons in f-subshell is:
- A. 14 (Correct)
- B. 10
- C. 6
- D. 7
Explanation: Seven orbitals each holding two electrons give 14.
Electronic order
96. The correct filling order among these is:
- A. 1s, 2s, 2p, 3s (Correct)
- B. 1s, 2p, 2s, 3s
- C. 1s, 2s, 3s, 2p
- D. 1s, 3s, 2s, 2p
Explanation: This follows increasing orbital energy.
Ion formation
97. When transition metals form cations, electrons are generally removed first from:
- A. ns orbital (Correct)
- B. (n-1)d orbital
- C. np orbital
- D. f orbital
Explanation: Though 4s fills before 3d, it is removed first during ionisation.
Exception logic
98. Chromium and copper are exceptions mainly because half-filled or fully filled subshells are:
- A. Relatively more stable (Correct)
- B. Always impossible
- C. Less stable than paired electrons
- D. Unaffected by exchange energy
Explanation: Extra stability comes from symmetry and exchange energy.
Chapter logic
99. Hund rule mainly helps predict:
- A. Distribution of electrons in degenerate orbitals (Correct)
- B. Nuclear charge
- C. Mass number
- D. Photon energy
Explanation: It determines how electrons occupy equal-energy orbitals.
Chapter logic
100. Electronic configuration acts as the bridge between atomic structure and:
- A. Periodic properties and bonding trends (Correct)
- B. Only nuclear reactions
- C. Only gas laws
- D. Only redox titration
Explanation: Outer-electron arrangement controls chemical behavior.
Quantum numbers
101. Which quantum number determines the size of orbital?
- A. Principal quantum number (Correct)
- B. Azimuthal quantum number
- C. Magnetic quantum number
- D. Spin quantum number
Explanation: Higher n usually means larger orbital size.
Quantum numbers
102. Which quantum number determines the shape of orbital?
- A. Azimuthal quantum number (Correct)
- B. Principal quantum number
- C. Magnetic quantum number
- D. Spin quantum number
Explanation: l determines whether the orbital is s, p, d, or f.
Quantum numbers
103. Which quantum number determines orientation in space?
- A. Magnetic quantum number (Correct)
- B. Spin quantum number
- C. Principal quantum number
- D. Mass number
Explanation: m differentiates orbitals of same subshell.
Quantum numbers
104. For n = 4, total number of orbitals in the shell is:
- A. 16 (Correct)
- B. 8
- C. 32
- D. 4
Explanation: Total orbitals in a shell = n$^2$.
Quantum numbers
105. For n = 3, total number of orbitals is:
- A. 9 (Correct)
- B. 18
- C. 3
- D. 6
Explanation: n$^2$ gives total orbital count.
Orbital identification
106. An orbital with n = 3 and l = 2 is:
- A. 3d (Correct)
- B. 3p
- C. 2d
- D. 4d
Explanation: l = 2 corresponds to d-subshell.
Orbital identification
107. An orbital with n = 2 and l = 0 is:
- A. 2s (Correct)
- B. 2p
- C. 1s
- D. 3s
Explanation: l = 0 denotes s-subshell.
Node logic
108. Number of radial nodes in 3p orbital is:
- A. 1 (Correct)
- B. 0
- C. 2
- D. 3
Explanation: n - l - 1 = 3 - 1 - 1 = 1.
Node logic
109. Number of angular nodes in 4d orbital is:
- A. 2 (Correct)
- B. 1
- C. 3
- D. 0
Explanation: Angular nodes equal l, and for d, l = 2.
Node logic
110. Total nodes in 4s orbital are:
- A. 3 (Correct)
- B. 0
- C. 1
- D. 4
Explanation: Total nodes = n - 1 = 3.
Magnetism
111. Species $Ne$ is:
- A. Diamagnetic (Correct)
- B. Paramagnetic
- C. Ferromagnetic
- D. Radioactive
Explanation: All electrons are paired in neon.
Magnetism
112. Species $O_2^-$ has unpaired electrons and is therefore:
- A. Paramagnetic (Correct)
- B. Diamagnetic
- C. Isoelectronic with Ne
- D. Noble
Explanation: Adding one electron to oxygen molecule still leaves one unpaired electron.
Emission
113. Emission spectrum appears as:
- A. Bright lines on dark background (Correct)
- B. Dark lines on bright background
- C. Only continuous band
- D. No visible pattern
Explanation: Emission occurs when excited atoms release light.
Absorption
114. Absorption spectrum appears as:
- A. Dark lines on bright background (Correct)
- B. Bright lines on dark background
- C. Single continuous green line
- D. Only X-ray spots
Explanation: Certain wavelengths are absorbed from a continuous source.
Wave-particle duality
115. Electron diffraction is evidence for:
- A. Wave nature of electrons (Correct)
- B. Only nuclear mass
- C. Positive charge of neutron
- D. Classical orbit
Explanation: Diffraction is a wave property.
Uncertainty
116. Greater certainty in position implies:
- A. Less certainty in momentum (Correct)
- B. More certainty in momentum
- C. No effect on momentum
- D. Higher charge
Explanation: This is the trade-off in uncertainty principle.
Energy ordering
117. Among 3s, 3p, and 3d orbitals of a multi-electron atom, increasing energy order is:
- A. 3s < 3p < 3d (Correct)
- B. 3d < 3p < 3s
- C. 3p < 3s < 3d
- D. 3s < 3d < 3p
Explanation: Within the same shell, energy increases with l for multi-electron atoms.
Energy ordering
118. Among 4s and 3d orbitals during filling, the lower energy is usually:
- A. 4s (Correct)
- B. 3d
- C. Both identical
- D. Depends only on spin
Explanation: n+l rule places 4s below 3d during filling.
Hydrogen-like energy
119. For hydrogen atom, energy depends only on:
- A. Principal quantum number n (Correct)
- B. Azimuthal quantum number only
- C. Magnetic quantum number only
- D. Spin only
Explanation: All orbitals with same n are degenerate in hydrogen.
Multi-electron atoms
120. In multi-electron atoms, orbitals of same n have different energies because of:
- A. Shielding and penetration (Correct)
- B. Only nuclear mass
- C. Planck constant
- D. Speed of light
Explanation: Electron-electron repulsion breaks the hydrogen-like degeneracy.
Photoelectric link
121. Threshold frequency in photoelectric effect means:
- A. Minimum frequency needed to eject electrons (Correct)
- B. Maximum frequency emitted by source
- C. Frequency at which intensity is zero
- D. Frequency equal to wavelength
Explanation: Below threshold, photons lack sufficient energy.
Photon relation
122. Increasing intensity of light below threshold frequency does not eject electrons because:
- A. Each photon still has insufficient energy (Correct)
- B. Intensity reduces work function
- C. More photons increase charge on nucleus
- D. Electrons stop absorbing energy
Explanation: Photon energy depends on frequency, not intensity.
NEET trap
123. An orbital and an orbit differ because an orbital is:
- A. A probability region, not a fixed path (Correct)
- B. Always circular
- C. Always planar
- D. Independent of quantum numbers
Explanation: Orbit is a Bohr path, orbital is a quantum mechanical region.
NEET trap
124. The set of quantum numbers not allowed for an electron is:
- A. n = 2, l = 2, m = 0, s = +1/2 (Correct)
- B. n = 3, l = 2, m = -1, s = -1/2
- C. n = 2, l = 1, m = 0, s = +1/2
- D. n = 1, l = 0, m = 0, s = -1/2
Explanation: For n = 2, l can only be 0 or 1.
Chapter integration
125. Atomic structure becomes NEET-friendly when you connect models, spectra, orbitals, and configurations through:
- A. Quantized energy and electron arrangement (Correct)
- B. Only memorised exceptions
- C. Only shell names
- D. Only mass number
Explanation: That single framework ties together the chapter.

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