{"id":12749,"date":"2025-09-22T13:22:26","date_gmt":"2025-09-22T12:22:26","guid":{"rendered":"https:\/\/mcqsadda.com\/?p=12749"},"modified":"2025-10-22T10:15:00","modified_gmt":"2025-10-22T09:15:00","slug":"atomic-structure-top-100-mcqs-with-answer-and-explanation","status":"publish","type":"post","link":"https:\/\/mcqsadda.com\/index.php\/2025\/09\/22\/atomic-structure-top-100-mcqs-with-answer-and-explanation\/","title":{"rendered":"Atomic structure Top 100 MCQs With Answer and Explanation"},"content":{"rendered":"\n

1. Who is regarded as the \u201cFather of Atomic Theory\u201d?
<\/mark><\/strong>A) J.J. Thomson
B) John Dalton
C) Ernest Rutherford
D) Niels Bohr
Answer: B<\/strong>
Explanation<\/strong>: John Dalton (1808) proposed the first modern atomic theory stating that matter is made up of indivisible particles called atoms.<\/p>\n\n\n\n

2. The discovery of the electron is credited to:
<\/mark><\/strong>A) Goldstein
B) J.J. Thomson
C) Rutherford
D) Bohr
Answer: B<\/strong>
Explanation<\/strong>: J.J. Thomson discovered the electron in 1897 using cathode ray tube experiments.<\/p>\n\n\n\n

3. The charge of a proton is:
<\/mark><\/strong>A) +1.6 \u00d7 10\u207b\u00b9\u2079 C
B) \u20131.6 \u00d7 10\u207b\u00b9\u2079 C
C) 0
D) 1 C
Answer: A<\/strong>
Explanation<\/strong>: A proton carries a positive elementary charge equal in magnitude to that of an electron but opposite in sign.<\/p>\n\n\n\n

4. The neutron was discovered by:
<\/mark><\/strong>A) Rutherford
B) Chadwick
C) Goldstein
D) Bohr
Answer: B<\/strong>
Explanation<\/strong>: James Chadwick discovered the neutron in 1932.<\/p>\n\n\n\n

5. The smallest unit of an element which retains its identity is called:
<\/mark><\/strong>A) Molecule
B) Atom
C) Ion
D) Proton
Answer: B<\/strong>
Explanation<\/strong>: An atom is the fundamental unit of matter that retains the chemical identity of the element.<\/p>\n\n\n\n

6. Cathode rays are streams of:
<\/mark><\/strong>A) Protons
B) Neutrons
C) Electrons
D) Alpha particles
Answer: C<\/strong>
Explanation<\/strong>: Cathode rays consist of negatively charged particles \u2013 electrons.<\/p>\n\n\n\n

7. Which subatomic particle has the least mass?
<\/strong><\/mark>A) Proton
B) Neutron
C) Electron
D) Positron
Answer: C<\/strong>
Explanation<\/strong>: The electron\u2019s mass is about 1\/1836 of a proton\u2019s mass.<\/p>\n\n\n\n

8. The nucleus of an atom consists of:
<\/mark><\/strong>A) Only protons
B) Protons and neutrons
C) Only neutrons
D) Protons and electrons
Answer: B<\/strong>
Explanation<\/strong>: The atomic nucleus is made up of protons and neutrons, known as nucleons.<\/p>\n\n\n\n

9. The positively charged rays in a discharge tube were discovered by:
<\/mark><\/strong>A) Thomson
B) Rutherford
C) Goldstein
D) Chadwick
Answer: C<\/strong>
Explanation<\/strong>: Goldstein discovered canal rays (positive rays), later identified as protons.<\/p>\n\n\n\n

10. The atomic number of an element represents:
<\/mark><\/strong>A) Number of neutrons
B) Number of protons
C) Sum of protons and neutrons
D) Number of isotopes
Answer: B<\/strong>
Explanation<\/strong>: Atomic number (Z) = number of protons in the nucleus = number of electrons in a neutral atom.<\/p>\n\n\n\n

11. Mass number (A) is equal to:
<\/strong><\/mark>A) Protons only
B) Neutrons only
C) Protons + Neutrons
D) Protons + Electrons
Answer: C<\/strong>
Explanation<\/strong>: Mass number A = number of protons (Z) + number of neutrons (N).<\/p>\n\n\n\n

12. Isotopes are atoms of the same element having:
<\/mark><\/strong>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<\/strong>
Explanation<\/strong>: Isotopes differ in neutrons but have same protons.<\/p>\n\n\n\n

13. Tritium is an isotope of hydrogen with:
<\/mark><\/strong>A) 1 proton, 0 neutrons
B) 1 proton, 1 neutron
C) 1 proton, 2 neutrons
D) 2 protons, 1 neutron
Answer: C<\/strong>
Explanation<\/strong>: Tritium has 1 proton and 2 neutrons (mass number 3).<\/p>\n\n\n\n

14. Which particle defines the chemical properties of an element?
<\/mark><\/strong>A) Proton
B) Neutron
C) Electron
D) Nucleus
Answer: C<\/strong>
Explanation<\/strong>: Electrons, especially valence electrons, determine chemical behavior.<\/p>\n\n\n\n

15. Which is heavier: neutron or proton?
<\/mark><\/strong>A) Proton
B) Neutron
C) Both equal
D) Cannot say
Answer: B<\/strong>
Explanation<\/strong>: Neutron has a slightly greater mass than proton.<\/p>\n\n\n\n

16. Which of the following is electrically neutral?
<\/mark><\/strong>A) Proton
B) Neutron
C) Electron
D) Positron
Answer: B<\/strong>
Explanation<\/strong>: Neutrons carry no charge.<\/p>\n\n\n\n

17. The electron was first named as \u201ccorpuscle\u201d by:
<\/mark><\/strong>A) Thomson
B) Rutherford
C) Bohr
D) Einstein
Answer: A<\/strong>
Explanation<\/strong>: J.J. Thomson called the electron a \u201ccorpuscle.\u201d<\/p>\n\n\n\n

18. The charge-to-mass ratio (e\/m) of electron was determined by:
<\/mark><\/strong>A) Rutherford
B) Millikan
C) Thomson
D) Bohr
Answer: C<\/strong>
Explanation<\/strong>: J.J. Thomson calculated the e\/m ratio of electron in 1897.<\/p>\n\n\n\n

19. The oil-drop experiment was performed by:
<\/mark><\/strong>A) Rutherford
B) Millikan
C) Goldstein
D) Bohr
Answer: B<\/strong>
Explanation<\/strong>: R.A. Millikan measured the charge of the electron with the oil-drop experiment.<\/p>\n\n\n\n

20. Which element has only one proton and no neutron?
<\/mark><\/strong>A) Helium
B) Hydrogen-1
C) Deuterium
D) Tritium
Answer: B<\/strong>
Explanation<\/strong>: Protium (\u00b9H) has 1 proton and 0 neutrons.<\/p>\n\n\n\n

21. The concept of indivisible atoms was first given by:
<\/mark><\/strong>A) Democritus
B) Dalton
C) Rutherford
D) Bohr
Answer: A<\/strong>
Explanation<\/strong>: Democritus (400 BC) coined the term \u201catomos\u201d meaning indivisible.<\/p>\n\n\n\n

22. Who discovered X-rays, which later helped in atomic studies?
<\/mark><\/strong>A) R\u00f6ntgen
B) Rutherford
C) Bohr
D) Chadwick
Answer: A<\/strong>
Explanation<\/strong>: Wilhelm R\u00f6ntgen discovered X-rays in 1895.<\/p>\n\n\n\n

23. The approximate radius of an atom is:
<\/mark><\/strong>A) 10\u207b\u00b9\u2070 m
B) 10\u207b\u00b9\u00b2 m
C) 10\u207b\u2076 m
D) 1 m
Answer: A<\/strong>
Explanation<\/strong>: Atomic radius is about 1 \u00c5 = 10\u207b\u00b9\u2070 m.<\/p>\n\n\n\n

24. The radius of the nucleus is about:
<\/mark><\/strong>A) 10\u207b\u00b9\u2075 m
B) 10\u207b\u00b9\u2070 m
C) 10\u207b\u2078 m
D) 10\u207b\u00b3 m
Answer: A<\/strong>
Explanation<\/strong>: Nuclear radius is ~10\u207b\u00b9\u2075 m (1 femtometer).<\/p>\n\n\n\n

25. The concept of \u201cplum pudding model\u201d was given by:
<\/mark><\/strong>A) Dalton
B) Thomson
C) Rutherford
D) Bohr
Answer: B<\/strong>
Explanation<\/strong>: J.J. Thomson proposed that electrons are embedded in a positively charged sphere (\u201cplum pudding\u201d model).<\/p>\n\n\n\n

26. Rutherford\u2019s alpha particle scattering experiment proved that:
<\/mark><\/strong>A) Atoms are indivisible
B) Atoms have no charge
C) Atoms have a dense central nucleus
D) Electrons revolve in shells
Answer: C<\/strong>
Explanation<\/strong>: Rutherford\u2019s experiment (1911) showed that most of the atom\u2019s mass and positive charge is concentrated in a tiny nucleus.<\/p>\n\n\n\n

27. In Rutherford\u2019s experiment, most alpha particles passed through the gold foil without deflection. This showed that:
<\/mark><\/strong>A) Atoms are hollow and empty
B) Atoms are solid spheres
C) Nucleus occupies whole atom
D) Electrons are inside nucleus
Answer: A<\/strong>
Explanation<\/strong>: Since most particles went undeflected, most of the atom is empty space.<\/p>\n\n\n\n

28. According to Rutherford\u2019s model, electrons:
<\/mark><\/strong>A) Are stationary inside atom
B) Revolve around the nucleus
C) Are embedded in the nucleus
D) Do not exist
Answer: B<\/strong>
Explanation<\/strong>: Rutherford proposed that electrons revolve around nucleus like planets around the sun.<\/p>\n\n\n\n

29. Major drawback of Rutherford\u2019s model was:
<\/mark><\/strong>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<\/strong>
Explanation<\/strong>: According to classical physics, orbiting electrons should radiate energy and fall into nucleus \u2013 instability problem.<\/p>\n\n\n\n

30. Bohr introduced the concept of:
<\/mark><\/strong>A) Stationary orbits
B) Neutrons
C) Atomic nucleus
D) Isotopes
Answer: A<\/strong>
Explanation<\/strong>: Bohr (1913) suggested electrons move in fixed orbits with quantized energy levels.<\/p>\n\n\n\n

31. Bohr\u2019s model successfully explained:
<\/mark><\/strong>A) Spectrum of hydrogen atom
B) Spectrum of all heavy atoms
C) Discovery of neutrons
D) Alpha scattering
Answer: A<\/strong>
Explanation<\/strong>: Bohr\u2019s model explains line spectra of hydrogen and hydrogen-like species.<\/p>\n\n\n\n

32. In Bohr\u2019s model, angular momentum of an electron is quantized and given by:
<\/mark><\/strong>A) mvr = nh\/2\u03c0
B) mvr = nh
C) mvr = h\/2\u03c0
D) mvr = n\u00b2h
Answer: A<\/strong>
Explanation<\/strong>: Bohr\u2019s postulate: angular momentum L = mvr = n(h\/2\u03c0).<\/p>\n\n\n\n

33. The energy of an electron in the nth orbit of hydrogen is proportional to:
<\/mark><\/strong>A) +1\/n\u00b2
B) \u20131\/n\u00b2
C) +n\u00b2
D) \u2013n
Answer: B<\/strong>
Explanation<\/strong>: Energy En = \u201313.6 eV\/n\u00b2 (negative sign shows bound state).<\/p>\n\n\n\n

34. Which of the following transitions gives the Lyman series in hydrogen?
<\/mark><\/strong>A) To n=2
B) To n=3
C) To n=1
D) To n=4
Answer: C<\/strong>
Explanation<\/strong>: Lyman series corresponds to electron transitions ending at n=1 (UV region).<\/p>\n\n\n\n

35. The Balmer series of hydrogen lies in the:
<\/mark><\/strong>A) Infrared region
B) Visible region
C) Ultraviolet region
D) X-ray region
Answer: B<\/strong>
Explanation<\/strong>: Balmer series (n\u21922) lies in visible region of electromagnetic spectrum.<\/p>\n\n\n\n

36. The Paschen series lies in:
<\/mark><\/strong>A) Visible region
B) UV region
C) Infrared region
D) Microwave region
Answer: C<\/strong>
Explanation<\/strong>: Paschen series corresponds to transitions to n=3 (infrared).<\/p>\n\n\n\n

37. Rydberg\u2019s constant for hydrogen is approximately:
<\/mark><\/strong>A) 1.097 \u00d7 10\u2077 m\u207b\u00b9
B) 6.022 \u00d7 10\u00b2\u00b3 mol\u207b\u00b9
C) 3 \u00d7 10\u2078 m\/s
D) 9.11 \u00d7 10\u207b\u00b3\u00b9 kg
Answer: A<\/strong>
Explanation<\/strong>: Rydberg constant R = 1.097 \u00d7 10\u2077 m\u207b\u00b9, used for calculating spectral lines.<\/p>\n\n\n\n

38. The principal quantum number (n) determines:
<\/mark><\/strong>A) Shape of orbital
B) Orientation of orbital
C) Size and energy of orbital
D) Spin of electron
Answer: C<\/strong>
Explanation<\/strong>: Principal quantum number (n=1,2,3\u2026) gives size and energy level of orbitals.<\/p>\n\n\n\n

39. The azimuthal quantum number (l) determines:<\/mark><\/strong>
A) Size of orbital
B) Shape of orbital
C) Energy of orbital only
D) Spin of orbital
Answer: B<\/strong>
Explanation<\/strong>: Azimuthal (angular momentum) quantum number l = 0,1,\u2026,(n\u20131) gives orbital shape (s,p,d,f).<\/p>\n\n\n\n

40. For l=2, the orbital is:
<\/mark><\/strong>A) s-orbital
B) p-orbital
C) d-orbital
D) f-orbital
Answer: C<\/strong>
Explanation<\/strong>: l=0 \u2192 s, l=1 \u2192 p, l=2 \u2192 d, l=3 \u2192 f.<\/p>\n\n\n\n

41. The magnetic quantum number (m) determines:
<\/mark><\/strong>A) Energy level
B) Shape of orbital
C) Orientation of orbital
D) Spin of orbital
Answer: C<\/strong>
Explanation<\/strong>: m ranges from \u2013l to +l, describing orientation of orbitals in space.<\/p>\n\n\n\n

42. For l=1, possible values of m are:
<\/mark><\/strong>A) 0
B) \u20131, 0, +1
C) \u20132, \u20131, 0, +1, +2
D) +1 only
Answer: B<\/strong>
Explanation<\/strong>: For l=1, m = \u20131,0,+1 \u2192 three p-orbitals (px, py, pz).<\/p>\n\n\n\n

43. The spin quantum number (s) has values:
<\/mark><\/strong>A) 0 and 1
B) +\u00bd and \u2013\u00bd
C) \u20131 and +1
D) \u20132 and +2
Answer: B<\/strong>
Explanation<\/strong>: Spin quantum number ms = +\u00bd (spin up), \u2013\u00bd (spin down).<\/p>\n\n\n\n

44. Maximum number of electrons in an orbital is:
<\/mark><\/strong>A) 1
B) 2
C) 3
D) 4
Answer: B<\/strong>
Explanation<\/strong>: Each orbital can hold maximum 2 electrons with opposite spins (Pauli principle).<\/p>\n\n\n\n

45. The maximum number of electrons in a shell with principal quantum number n is:
<\/mark><\/strong>A) 2n
B) 2n\u00b2
C) n\u00b2
D) n\u00b3
Answer: B<\/strong>
Explanation<\/strong>: Each shell can hold maximum 2n\u00b2 electrons.<\/p>\n\n\n\n

46. The 3rd shell (n=3) can hold a maximum of:
<\/mark><\/strong>A) 8 electrons
B) 18 electrons
C) 32 electrons
D) 50 electrons
Answer: B<\/strong>
Explanation<\/strong>: Maximum electrons in n=3 \u2192 2n\u00b2 = 2\u00d79 = 18.<\/p>\n\n\n\n

47. The number of orbitals in a subshell with quantum number l is:
<\/mark><\/strong>A) 2l+1
B) 2n\u00b2
C) n\u00b2
D) 2n+1
Answer: A<\/strong>
Explanation<\/strong>: Number of orbitals in subshell = 2l+1.<\/p>\n\n\n\n

48. How many orbitals are possible in the d-subshell?
<\/mark><\/strong>A) 3
B) 5
C) 7
D) 9
Answer: B<\/strong>
Explanation<\/strong>: For l=2 (d), number of orbitals = 2l+1 = 5.<\/p>\n\n\n\n

49. Maximum electrons in f-subshell is:
<\/mark><\/strong>A) 7
B) 14
C) 10
D) 18
Answer: B<\/strong>
Explanation<\/strong>: f-subshell has 7 orbitals \u2192 max 14 electrons.<\/p>\n\n\n\n

50. If n=4, l=2, number of orbitals possible is:
<\/mark><\/strong>A) 3
B) 5
C) 7
D) 9
Answer: B<\/strong>
Explanation<\/strong>: For l=2, orbitals = 2l+1 = 5 (d-orbitals in 4th shell).<\/p>\n\n\n\n

51. The arrangement of electrons in shells and subshells of an atom is called:
<\/mark><\/strong>A) Atomic structure
B) Electronic configuration
C) Isotopy
D) Valency
Answer: B<\/strong>
Explanation<\/strong>: The distribution of electrons among orbitals of an atom is called electronic configuration.<\/p>\n\n\n\n

52. Which principle states that no two electrons in an atom can have all four quantum numbers identical?
<\/mark><\/strong>A) Hund\u2019s rule
B) Pauli exclusion principle
C) Aufbau principle
D) Heisenberg principle
Answer: B<\/strong>
Explanation<\/strong>: Pauli exclusion principle states that each orbital can hold maximum 2 electrons with opposite spins.<\/p>\n\n\n\n

53. Aufbau principle is concerned with:
<\/mark><\/strong>A) Stability of nucleus
B) Order of filling orbitals
C) Shape of orbitals
D) Orientation of orbitals
Answer: B<\/strong>
Explanation<\/strong>: Aufbau principle explains the sequence in which orbitals are filled with electrons (lowest energy first).<\/p>\n\n\n\n

54. According to Aufbau principle, which orbital fills after 3p?
<\/mark><\/strong>A) 3d
B) 4s
C) 4p
D) 4f
Answer: B<\/strong>
Explanation<\/strong>: Order of filling: 1s \u2192 2s \u2192 2p \u2192 3s \u2192 3p \u2192 4s \u2192 3d \u2026<\/p>\n\n\n\n

55. Which rule states that electrons occupy orbitals singly first before pairing?
<\/mark><\/strong>A) Pauli exclusion principle
B) Hund\u2019s rule of maximum multiplicity
C) Aufbau principle
D) Octet rule
Answer: B<\/strong>
Explanation<\/strong>: Hund\u2019s rule: In degenerate orbitals, electrons fill singly with parallel spins before pairing.<\/p>\n\n\n\n

56. The ground-state electronic configuration of oxygen (Z=8) is:
<\/mark><\/strong>A) 1s\u00b2 2s\u00b2 2p\u2076
B) 1s\u00b2 2s\u00b2 2p\u2074
C) 1s\u00b2 2s\u00b9 2p\u2075
D) 1s\u00b2 2s\u00b2 2p\u00b3
Answer: B<\/strong>
Explanation<\/strong>: Oxygen has 8 electrons: 1s\u00b2 2s\u00b2 2p\u2074.<\/p>\n\n\n\n

57. The electronic configuration of sodium (Z=11) is:
<\/mark><\/strong>A) 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b9
B) 1s\u00b2 2s\u00b2 2p\u2075 3s\u00b2
C) 1s\u00b2 2s\u00b2 2p\u2076
D) 1s\u00b2 2s\u00b2 2p\u00b3
Answer: A<\/strong>
Explanation<\/strong>: Sodium: 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b9 (outermost electron in 3s).<\/p>\n\n\n\n

58. Which element has configuration [He]2s\u00b22p\u00b2?
<\/mark><\/strong>A) Beryllium
B) Boron
C) Carbon
D) Nitrogen
Answer: C<\/strong>
Explanation<\/strong>: Carbon (Z=6) has 1s\u00b22s\u00b22p\u00b2.<\/p>\n\n\n\n

59. Which element has a half-filled p-subshell?
<\/mark><\/strong>A) Boron (Z=5)
B) Nitrogen (Z=7)
C) Oxygen (Z=8)
D) Fluorine (Z=9)
Answer: B<\/strong>
Explanation<\/strong>: Nitrogen: 1s\u00b2 2s\u00b2 2p\u00b3 \u2192 half-filled 2p subshell.<\/p>\n\n\n\n

60. The configuration of chlorine (Z=17) is:
<\/mark><\/strong>A) 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2075
B) 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2076
C) 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2074
D) 1s\u00b2 2s\u00b2 2p\u2075 3s\u00b2 3p\u2076
Answer: A<\/strong>
Explanation<\/strong>: Chlorine has 17 electrons \u2192 1s\u00b2 2s\u00b2 2p\u2076 3s\u00b2 3p\u2075.<\/p>\n\n\n\n

61. The general electronic configuration of alkali metals is:
<\/mark><\/strong>A) ns\u00b9
B) ns\u00b2
C) ns\u00b2 np\u2076
D) ns\u00b2 np\u00b9
Answer: A<\/strong>
Explanation<\/strong>: Alkali metals have one electron in outermost s-orbital (ns\u00b9).<\/p>\n\n\n\n

62. Which of the following has an outer electronic configuration of ns\u00b2 np\u2075?
<\/mark><\/strong>A) Alkali metals
B) Alkaline earth metals
C) Halogens
D) Noble gases
Answer: C<\/strong>
Explanation<\/strong>: Halogens have 7 valence electrons (ns\u00b2np\u2075).<\/p>\n\n\n\n

63. Noble gases have the general configuration:
<\/mark><\/strong>A) ns\u00b2 np\u00b9
B) ns\u00b2 np\u2075
C) ns\u00b2 np\u2076
D) ns\u00b2 np\u00b3
Answer: C<\/strong>
Explanation<\/strong>: Noble gases have complete octets \u2192 ns\u00b2 np\u2076 (except helium: 1s\u00b2).<\/p>\n\n\n\n

64. The electronic configuration of calcium (Z=20) is:
<\/mark><\/strong>A) [Ar]4s\u00b2
B) [Ne]3s\u00b2 3p\u2076 3d\u00b2
C) [Ar]3d\u00b2
D) [Ne]3s\u00b2 3p\u2075
Answer: A<\/strong>
Explanation<\/strong>: Calcium: 1s\u00b22s\u00b22p\u20763s\u00b23p\u20764s\u00b2 \u2192 [Ar]4s\u00b2.<\/p>\n\n\n\n

65. Which has an anomalous configuration due to half-filled stability?
<\/mark><\/strong>A) Zn (Z=30)
B) Cr (Z=24)
C) Ca (Z=20)
D) Ne (Z=10)
Answer: B<\/strong>
Explanation<\/strong>: Chromium: [Ar]3d\u20754s\u00b9 instead of [Ar]3d\u20744s\u00b2 (extra stability of half-filled 3d).<\/p>\n\n\n\n

66. Copper (Z=29) has electronic configuration:
<\/mark><\/strong>A) [Ar]3d\u20794s\u00b2
B) [Ar]3d\u00b9\u20704s\u00b9
C) [Ar]3d\u00b9\u20704s\u00b2
D) [Ar]3d\u20784s\u00b2
Answer: B<\/strong>
Explanation<\/strong>: Copper: [Ar]3d\u00b9\u20704s\u00b9 (due to stability of fully-filled d-orbital).<\/p>\n\n\n\n

67. The maximum number of electrons that can be filled in 3d subshell is:
<\/mark><\/strong>A) 8
B) 10
C) 12
D) 14
Answer: B<\/strong>
Explanation<\/strong>: d-subshell has 5 orbitals, each holds 2 electrons \u2192 max 10.<\/p>\n\n\n\n

68. Which orbital will be filled first according to Aufbau rule?
<\/mark><\/strong>A) 4s
B) 3d
C) 4p
D) 5s
Answer: A<\/strong>
Explanation<\/strong>: 4s has lower energy than 3d, so it fills first.<\/p>\n\n\n\n

69. Which among the following represents the correct order of filling of orbitals?
<\/mark><\/strong>A) 3p \u2192 3d \u2192 4s
B) 3p \u2192 4s \u2192 3d
C) 4s \u2192 3p \u2192 3d
D) 3d \u2192 3p \u2192 4s
Answer: B<\/strong>
Explanation<\/strong>: Correct order: 3p \u2192 4s \u2192 3d (Aufbau principle).<\/p>\n\n\n\n

70. According to Pauli exclusion principle, the two electrons in the same orbital differ in:
<\/mark><\/strong>A) n
B) l
C) m
D) s (spin quantum number)
Answer: D<\/strong>
Explanation<\/strong>: Two electrons in same orbital must have opposite spins.<\/p>\n\n\n\n

71. Which of the following orbitals will have the lowest energy?
<\/mark><\/strong>A) 3d
B) 4s
C) 4p
D) 5s
Answer: B<\/strong>
Explanation<\/strong>: 4s has slightly lower energy than 3d (exceptions exist for transition metals).<\/p>\n\n\n\n

72. The configuration of Fe (Z=26) is:
<\/mark><\/strong>A) [Ar]3d\u20744s\u00b2
B) [Ar]3d\u20764s\u00b2
C) [Ar]3d\u20754s\u00b9
D) [Ar]3d\u20774s\u00b9
Answer: B<\/strong>
Explanation<\/strong>: Iron: 1s\u00b22s\u00b22p\u20763s\u00b23p\u20763d\u20764s\u00b2 \u2192 [Ar]3d\u20764s\u00b2.<\/p>\n\n\n\n

73. Which element has completely filled d-subshell in its ground state?
<\/mark><\/strong>A) Sc (Z=21)
B) Zn (Z=30)
C) Cr (Z=24)
D) Cu (Z=29)
Answer: B<\/strong>
Explanation<\/strong>: Zn: [Ar]3d\u00b9\u20704s\u00b2 \u2192 fully filled d-orbital.<\/p>\n\n\n\n

74. The number of unpaired electrons in nitrogen (Z=7) is:
<\/mark><\/strong>A) 1
B) 2
C) 3
D) 4
Answer: C<\/strong>
Explanation<\/strong>: N: 1s\u00b22s\u00b22p\u00b3 \u2192 three unpaired electrons in 2p orbitals.<\/p>\n\n\n\n

75. Which of the following elements has a stable octet configuration in its ground state?
<\/mark><\/strong>A) Oxygen
B) Neon
C) Sodium
D) Chlorine
Answer: B<\/strong>
Explanation<\/strong>: Neon (Z=10) has a full octet (1s\u00b22s\u00b22p\u2076). Hence chemically inert.<\/p>\n\n\n\n

76. Which scientist proposed the wave nature of electrons?
<\/mark><\/strong>A) Bohr
B) Heisenberg
C) de Broglie
D) Planck
Answer: C<\/strong>
Explanation<\/strong>: Louis de Broglie (1924) proposed electrons behave like waves with wavelength \u03bb = h\/p.<\/p>\n\n\n\n

77. The de Broglie wavelength of a particle is given by:
<\/mark><\/strong>A) \u03bb = h\/mv
B) \u03bb = mv\/h
C) \u03bb = h\u03bd
D) \u03bb = c\/\u03bd
Answer: A<\/strong>
Explanation<\/strong>: De Broglie wavelength \u03bb = h\/p = h\/(mv).<\/p>\n\n\n\n

78. The uncertainty principle was given by:
<\/mark><\/strong>A) Planck
B) Bohr
C) Heisenberg
D) Schr\u00f6dinger
Answer: C<\/strong>
Explanation<\/strong>: Heisenberg\u2019s Uncertainty Principle: \u0394x\u00b7\u0394p \u2265 h\/4\u03c0.<\/p>\n\n\n\n

79. The uncertainty principle is significant only for:
<\/mark><\/strong>A) Macroscopic objects
B) Microscopic particles like electrons
C) Planets
D) Satellites
Answer: B<\/strong>
Explanation<\/strong>: Uncertainty is negligible for large bodies but important for atomic particles.<\/p>\n\n\n\n

80. Schr\u00f6dinger equation deals with:
<\/mark><\/strong>A) Particle nature of electron
B) Wave nature of electron
C) Nuclear reactions
D) Spectroscopy of atoms
Answer: B<\/strong>
Explanation<\/strong>: Schr\u00f6dinger wave equation describes the wave behavior of electrons in atoms.<\/p>\n\n\n\n

81. Quantum mechanical model of the atom was developed by:
<\/mark><\/strong>A) Bohr
B) Schr\u00f6dinger
C) Rutherford
D) Thomson
Answer: B<\/strong>
Explanation: Schr\u00f6dinger\u2019s model is the most accepted atomic model.<\/p>\n\n\n\n

82. Atomic orbital is defined as:
<\/mark><\/strong>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<\/strong>
Explanation<\/strong>: Orbital is a 3D region of maximum electron probability (90%).<\/p>\n\n\n\n

83. The s-orbital is:
<\/mark><\/strong>A) Dumbbell shaped
B) Spherical
C) Double dumbbell
D) Complex shape
Answer: B<\/strong>
Explanation<\/strong>: s-orbitals are spherical in shape.<\/p>\n\n\n\n

84. The p-orbitals are:
<\/mark><\/strong>A) Spherical
B) Dumbbell shaped
C) Double dumbbell
D) Spherical with nodes
Answer: B<\/strong>
Explanation<\/strong>: p-orbitals (px, py, pz) are dumbbell-shaped.<\/p>\n\n\n\n

85. The d-orbitals are:
<\/mark><\/strong>A) Dumbbell shaped
B) Spherical
C) Double dumbbell\/complex
D) Circular
Answer: C<\/strong>
Explanation<\/strong>: d-orbitals have double dumbbell or cloverleaf shapes.<\/p>\n\n\n\n

86. Number of nodal planes in p-orbital is:
<\/mark><\/strong>A) 0
B) 1
C) 2
D) 3
Answer: B<\/strong>
Explanation<\/strong>: p-orbital has one nodal plane passing through nucleus.<\/p>\n\n\n\n

87. The number of radial nodes in an orbital is given by:
<\/mark><\/strong>A) n\u2013l\u20131
B) n+l
C) 2l+1
D) l\u20131
Answer: A<\/strong>
Explanation<\/strong>: Radial nodes = n \u2013 l \u2013 1.<\/p>\n\n\n\n

88. The number of angular nodes is equal to:
<\/mark><\/strong>A) n\u2013l\u20131
B) l
C) n\u00b2
D) 2l+1
Answer: B<\/strong>
Explanation<\/strong>: Angular nodes depend on azimuthal quantum number (l).<\/p>\n\n\n\n

89. The total number of nodes in an orbital is:
<\/mark><\/strong>A) n\u20131
B) n\u00b2
C) 2n
D) l\u20131
Answer: A<\/strong>
Explanation<\/strong>: Total nodes = n \u2013 1 = (radial + angular).<\/p>\n\n\n\n

90. Which orbital has no nodes?
<\/mark><\/strong>A) 1s
B) 2s
C) 2p
D) 3p
Answer: A<\/strong>
Explanation<\/strong>: 1s orbital has n=1, total nodes = 0.<\/p>\n\n\n\n

91. Which orbital has spherical symmetry?
<\/mark><\/strong>A) p
B) d
C) f
D) s
Answer: D<\/strong>
Explanation<\/strong>: s-orbitals are spherically symmetric around the nucleus.<\/p>\n\n\n\n

92. Maximum number of electrons in 4f-subshell is:
<\/mark><\/strong>A) 7
B) 10
C) 14
D) 18
Answer: C<\/strong>
Explanation<\/strong>: f-subshell has 7 orbitals \u2192 max 14 electrons.<\/p>\n\n\n\n

93. Degenerate orbitals are orbitals having:
<\/mark><\/strong>A) Same shape
B) Same energy
C) Same nucleus
D) Same orientation
Answer: B<\/strong>
Explanation<\/strong>: Orbitals with same energy are called degenerate (e.g., px, py, pz).<\/p>\n\n\n\n

94. Which of the following orbitals does not exist?
<\/mark><\/strong>A) 1p
B) 2p
C) 3d
D) 4f
Answer: A<\/strong>
Explanation<\/strong>: For n=1, l=0 only (s-orbital). 1p does not exist.<\/p>\n\n\n\n

95. Which set of quantum numbers is not possible?
<\/mark><\/strong>A) n=3, l=2, m=0, s=+\u00bd
B) n=2, l=1, m=+1, s=\u2013\u00bd
C) n=1, l=0, m=0, s=+\u00bd
D) n=3, l=3, m=0, s=+\u00bd
Answer: D<\/strong>
Explanation<\/strong>: For n=3, maximum l = n\u20131 = 2. So l=3 is not possible.<\/p>\n\n\n\n

96. Which scientist proposed the dual nature of radiation?
<\/mark><\/strong>A) Einstein
B) Planck
C) Bohr
D) de Broglie
Answer: B<\/strong>
Explanation<\/strong>: Max Planck proposed quantum theory of radiation (1900), Einstein later explained photoelectric effect (1905).<\/p>\n\n\n\n

97. Einstein explained the photoelectric effect using the concept of:
<\/mark><\/strong>A) Wave theory
B) Particle (photon) nature of light
C) String theory
D) Quantum mechanical model
Answer: B<\/strong>
Explanation<\/strong>: Einstein used photon theory: light is made of discrete packets (photons).<\/p>\n\n\n\n

98. The energy of a photon is given by:
<\/mark><\/strong>A) E = h\/\u03bb
B) E = h\u03bd
C) E = mc\u00b2
D) E = h\u00b2\/2m
Answer: B<\/strong>
Explanation<\/strong>: Energy of photon = h\u03bd = hc\/\u03bb.<\/p>\n\n\n\n

99. The frequency of a photon with wavelength 600 nm is approximately:
<\/mark><\/strong>A) 3 \u00d7 10\u00b9\u2075 Hz
B) 5 \u00d7 10\u00b9\u2074 Hz
C) 6 \u00d7 10\u00b9\u00b2 Hz
D) 5 \u00d7 10\u00b9\u2076 Hz
Answer: B<\/strong>
Explanation<\/strong>: \u03bd = c\/\u03bb = 3\u00d710\u2078 \/ 600\u00d710\u207b\u2079 \u2248 5\u00d710\u00b9\u2074 Hz.<\/p>\n\n\n\n

100. Which atomic model is the most widely accepted today?
<\/mark><\/strong>A) Rutherford model
B) Bohr model
C) Quantum mechanical model
D) Plum pudding model
Answer: C<\/strong>
Explanation<\/strong>: The quantum mechanical model (Schr\u00f6dinger\u2019s model) is the modern accepted model of the atom.<\/p>\n","protected":false},"excerpt":{"rendered":"

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