Class 12 Physics Ch-12 Atoms MCQs Exam 2027

Chapter: Atoms

Topic 1: $\alpha$-particle Scattering & Rutherford’s Model

1. Rutherford’s $\alpha$-particle scattering experiment was responsible for the discovery of: [BSEB, 2016 (A)]

   (A) Electron

   (B) Nucleus

   (C) Proton

   (D) Neutron

2. The force responsible for the scattering of $\alpha$-particles in Rutherford’s experiment is: [BSEB, 2021 (A)]

   (A) Gravitational force

   (B) Coulomb force

   (C) Nuclear force

   (D) Magnetic force

3. The size of an atom is approximately of the order of: [BSEB, 2012 (A)]

   (A) $10^{-10}$ m

   (B) $10^{-15}$ m

   (C) $10^{-8}$ m

   (D) $10^{-12}$ m

4. According to Rutherford, most of the space inside the atom is: [BSEB, 2020 (A)]

   (A) Solid

   (B) Hollow

   (C) Positively charged

   (D) Negatively charged

5. The order of the radius of the nucleus of an atom is: [BSEB, 2014 (A)]

   (A) $10^{-15}$ m

   (B) $10^{-10}$ m

   (C) $10^{-8}$ m

   (D) $10^{-12}$ m

6. The charge on an $\alpha$-particle is: [BSEB, 2019 (A)]

   (A) $+e$

   (B) $+2e$

   (C) $+4e$

   (D) $-e$

7. In Rutherford’s model, the path of an electron was assumed to be:

   (A) Circular

   (B) Elliptical

   (C) Parabolic

   (D) Linear

8. In the gold foil experiment, $\alpha$-particles are deflected because:

   (A) The nucleus is heavy

   (B) The nucleus is positively charged

   (C) Electrons are light

   (D) The atom is empty

9. When the impact parameter is zero, the scattering angle is:

   (A) $0^\circ$

   (B) $90^\circ$

   (C) $180^\circ$

   (D) $45^\circ$

10. Which model failed to explain the stability of an atom? [BSEB, 2018 (A)]

    (A) Rutherford Model

    (B) Bohr Model

    (C) Thomson Model

    (D) Quantum Model

Topic 2: Bohr’s Atomic Model & Angular Momentum

11. 11. The minimum angular momentum of an electron in a Hydrogen atom is: [BSEB, 2018, 2021]

        (A) $h/\pi$

        (B) $h/2\pi$

        (C) $h/4\pi$

        (D) $2\pi/h$

12. Bohr’s frequency condition is: [BSEB, 2021 (A)]

    (A) $E_2 – E_1 = h\nu$

    (B) $E_2 – E_1 = 1/2 h\nu$

    (C) $E_1 – E_2 = h\nu$

    (D) $E_2 + E_1 = h\nu$

13. The relation between the radius of the $n^{th}$ orbit ($r_n$) and $n$ is: [BSEB, 2018, 2022]

    (A) $r_n \propto n$

    (B) $r_n \propto n^2$

    (C) $r_n \propto 1/n$

    (D) $r_n \propto 1/n^2$

14. As the principal quantum number $n$ increases, the radius of the orbit: [BSEB, 2020 (A)]

    (A) Increases

    (B) Decreases

    (C) Remains constant

    (D) First increases then decreases

15. The ratio of the speed of an electron in the first orbit of H-atom to the speed of light is: [BSEB, 2021 (A)]

    (A) $1/137$

    (B) $1/2$

    (C) $1/237$

    (D) $1/100$

16. The condition for a stable orbit according to Bohr’s theory is: [BSEB, 2019 (A)]

    (A) $mvr = nh/2\pi$

    (B) $mvr = nh/\pi$

    (C) $mvr = n^2h/2\pi$

    (D) $mvr = h/2\pi$

17. Bohr’s model is based on: [BSEB, 2017 (A)]

    (A) Classical Physics

    (B) Quantum Theory

    (C) Relativity Theory

    (D) None of these

18. The radius of the second orbit of a Hydrogen atom is how many times the first orbit? [BSEB, 2023 (A)]

    (A) 2 times

    (B) 4 times

    (C) 8 times

    (D) 16 times

19. Bohr’s model is valid for: [BSEB, 2016 (A)]

    (A) Only Hydrogen atom

    (B) Hydrogen-like ions ($He^+$, $Li^{++}$)

    (C) Simple Helium atom

    (D) Both (A) and (B)

20. The dimensions of angular momentum are:

    (A) $[ML^2T^{-1}]$

    (B) $[MLT^{-1}]$

    (C) $[ML^2T^{-2}]$

    (D) $[M^0L^2T^{-1}]$

21. The relation between the velocity $v_n$ in the $n^{th}$ orbit and $n$ is:

    (A) $v_n \propto n$

    (B) $v_n \propto 1/n$

    (C) $v_n \propto n^2$

    (D) $v_n \propto 1/n^2$

22. The value of Bohr radius $a_0$ is: [BSEB, 2020 (A)]

    (A) 0.53 Å

    (B) 0.35 Å

    (C) 0.85 Å

    (D) 1.0 Å

23. The angular momentum in the $n=2$ level will be: [BSEB, 2022 (A)]

    (A) $h/\pi$

    (B) $h/2\pi$

    (C) $2h/\pi$

    (D) $3h/2\pi$

24. In Bohr’s model, the centripetal force is provided by:

    (A) Coulomb attraction

    (B) Gravitation

    (C) Nuclear force

    (D) External electric field

25. An electron orbit is called “stationary” if:

    (A) It does not radiate energy

    (B) Its velocity is zero

    (C) It is near the nucleus

    (D) It emits energy continuously

Topic 3: Atomic Energy Levels & Ionization

26. The energy of a Hydrogen atom in its ground state is: [BSEB, 2018 (A)]

    (A) $-13.6$ eV

    (B) $+13.6$ eV

    (C) $-3.4$ eV

    (D) $0$ eV

27. The value of energy in the excited state $n=2$ is: [BSEB, 2020 (A)]

    (A) $-13.6$ eV

    (B) $-3.4$ eV

    (C) $-1.51$ eV

    (D) $-0.85$ eV

28. The ionization potential for a Hydrogen atom is: [BSEB, 2021 (A)]

    (A) $13.6$ V

    (B) $10.2$ V

    (C) $3.4$ V

    (D) $1.51$ V

29. The relation between kinetic energy ($K$) and total energy ($E$) is: [BSEB, 2024 (A)]

    (A) $K = -E$

    (B) $K = E$

    (C) $K = 2E$

    (D) $K = E/2$

30. The relation between potential energy ($U$) and total energy ($E$) is:

    (A) $U = 2E$

    (B) $U = -2E$

    (C) $U = E$

    (D) $U = -E$

31. The $n=3$ energy level is called:

    (A) First excited state

    (B) Second excited state

    (C) Third excited state

    (D) Ground state

32. How much energy is required to ionize a Hydrogen atom? [BSEB, 2017 (A)]

    (A) $13.6$ eV

    (B) $10.2$ eV

    (C) $12.1$ eV

    (D) $3.4$ eV

33. Electron-volt ($eV$) is a unit of: [BSEB, 2016, 2020]

    (A) Energy

    (B) Potential

    (C) Current

    (D) Power

34. The average lifetime of an excited state of an atom is:

    (A) $10^{-8}$ s

    (B) $10^{-6}$ s

    (C) $10^{-10}$ s

    (D) $1$ s

35. As the principal quantum number $n$ increases, the difference between energy levels:

    (A) Increases

    (B) Decreases

    (C) Remains the same

    (D) Becomes zero

36. The energy in the first orbit of $He^+$ ion ($Z=2$) will be:

    (A) $-13.6$ eV

    (B) $-54.4$ eV

    (C) $-27.2$ eV

    (D) $-6.8$ eV

37. The excitation potential for $n=1$ to $n=2$ is:

    (A) $10.2$ V

    (B) $12.1$ V

    (C) $13.6$ V

    (D) $3.4$ V

38. If the ground state radius of H-atom is $r_0$, the radius of the $n^{th}$ orbit is: [BSEB, 2022 (A)]

    (A) $n r_0$

    (B) $n^2 r_0$

    (C) $r_0/n$

    (D) $r_0/n^2$

39. What does the negative energy of an electron signify?

    (A) The electron is bound to the nucleus

    (B) The electron is free

    (C) The electron is inside the nucleus

    (D) The electron does not exist

40. 1 eV is equal to: [BSEB, 2020 (A)]

    (A) $1.6 \times 10^{-19}$ J

    (B) $1.6 \times 10^{19}$ J

    (C) $6.6 \times 10^{-34}$ J

    (D) $9.1 \times 10^{-31}$ J

Topic 4: Hydrogen Spectrum

41. Which series of the Hydrogen spectrum lies in the visible region? [BSEB, 2013, 2019, 2020, 2024]

    (A) Lyman series

    (B) Balmer series

    (C) Paschen series

    (D) Brackett series

42. Lyman series is found in which region? [BSEB, 2012, 2023]

    (A) Ultraviolet (UV) region

    (B) Visible region

    (C) Infrared region

    (D) X-ray region

43. Paschen series is found in which region of the spectrum? [BSEB, 2020 (A)]

    (A) Ultraviolet

    (B) Visible

    (C) Infrared

    (D) Gamma rays

44. The value of $n_1$ for the Balmer series is:

    (A) 1

    (B) 2

    (C) 3

    (D) 4

45. Which series of H-spectrum does NOT lie in the infrared region? [BSEB, 2017 (A)]

    (A) Lyman series

    (B) Paschen series

    (C) Brackett series

    (D) Pfund series

46. The value of Rydberg constant ($R$) is:

    (A) $1.097 \times 10^7$ m$^{-1}$

    (B) $1.097 \times 10^{-7}$ m$^{-1}$

    (C) $1.097 \times 10^5$ m$^{-1}$

    (D) $1.097$ m$^{-1}$

47. The unit of Rydberg constant is: [BSEB, 2022 (A)]

    (A) m

    (B) m$^{-1}$

    (C) s

    (D) J

48. For the first line of the Lyman series, the value of $n_2$ is:

    (A) 2

    (B) 3

    (C) 4

    (D) $\infty$

49. $H_\alpha$ line belongs to which series?

    (A) Lyman

    (B) Balmer

    (C) Paschen

    (D) Brackett

50. The formula for Wave Number is:

    (A) $1/\lambda = R(1/n_1^2 – 1/n_2^2)$

    (B) $\lambda = R(1/n_1^2 – 1/n_2^2)$

    (C) $1/\lambda = R(n_1^2 – n_2^2)$

    (D) $1/\lambda = (1/n_1^2 – 1/n_2^2)/R$

51. What are the dark lines present in the Solar spectrum called? [BSEB, 2018 (A)]

    (A) Fraunhofer lines

    (B) Balmer lines

    (C) Lyman lines

    (D) Emission lines

52. Continuous Spectrum is obtained from: [BSEB, 2021 (A)]

    (A) Hot solids

    (B) Discharge tube

    (C) Sodium vapor

    (D) None of these

53. The dimensions of Rydberg constant are: [BSEB, 2021 (A)]

    (A) $[L^{-1}]$

    (B) $[L]$

    (C) $[T^{-1}]$

    (D) $[M]$

54. For the series limit, the value of $n_2$ is:

    (A) 0

    (B) 1

    (C) $\infty$

    (D) 100

55. The value of $n_1$ for the Brackett series is:

    (A) 3

    (B) 4

    (C) 5

    (D) 2

56. Who first explained the Hydrogen spectrum? [BSEB, 2015 (A)]

    (A) Bohr

    (B) Rutherford

    (C) Dalton

    (D) Thomson

57. Pfund series is found in:

    (A) Ultraviolet region

    (B) Far-Infrared region

    (C) Visible region

    (D) X-rays

58. The color of the $H_\alpha$ line is:

    (A) Red

    (B) Blue

    (C) Violet

    (D) Yellow

59. Ionization frequency in terms of Rydberg constant ($R$) and speed of light ($c$) is:

    (A) $Rc$

    (B) $R/c$

    (C) $c/R$

    (D) $R+c$

60. If an electron transitions from $n=3$ to $n=2$, the wavelength of emitted photon is:

    (A) $36/5R$

    (B) $5/36R$

    (C) $1/R$

    (D) $4/R$

Topic 5: Structure of Atom & General Properties

61. Thomson’s model is also known as:

    (A) Plum Pudding Model

    (B) Solar System Model

    (C) Nuclear Model

    (D) Quantum Model

62. Cathode rays are made up of: [BSEB, 2021 (A)]

    (A) Electrons

    (B) Protons

    (C) Neutrons

    (D) Photons

63. Who discovered the electron? [BSEB, 2014 (A)]

    (A) J.J. Thomson

    (B) Chadwick

    (C) Goldstein

    (D) Rutherford

64. The ratio of charge to mass ($e/m$) of an electron is called: [BSEB, 2022 (A)]

    (A) Specific charge

    (B) Angular momentum

    (C) Magnetic moment

    (D) Planck’s constant

65. Electrically, an atom is: [BSEB, 2017 (A)]

    (A) Neutral

    (B) Positively charged

    (C) Negatively charged

    (D) Unstable

66. Atomic number $Z$ is equal to:

    (A) Number of protons

    (B) Number of neutrons

    (C) Mass number

    (D) Both (A) and (B)

67. According to Bohr’s model, kinetic energy $K_n$ of an electron $\propto$:

    (A) $1/n^2$

    (B) $1/n$

    (C) $n^2$

    (D) $n$

68. When is the total energy of an electron zero?

    (A) When it is near the nucleus

    (B) When it is at infinite distance from the atom

    (C) When it is in the ground state

    (D) Never

69. The radius of the third orbit of H-atom is (where $r_1$ is first orbit radius):

    (A) $9 r_1$

    (B) $3 r_1$

    (C) $27 r_1$

    (D) $r_1/3$

70. The energy of the second Bohr orbit will be:

    (A) $-13.6/2$ eV

    (B) $-13.6/4$ eV

    (C) $-13.6 \times 4$ eV

    (D) $-3.4$ eV

71. Absorption spectrum is obtained when:

    (A) White light is passed through a cold gas

    (B) Gas is heated

    (C) Metal is heated

    (D) None of these

72. Which transition will emit a photon of maximum frequency?

    (A) $n=2 \rightarrow n=1$

    (B) $n=3 \rightarrow n=2$

    (C) $n=4 \rightarrow n=3$

    (D) $n=10 \rightarrow n=9$

73. How many spectral lines are possible for H-atom from $n=4$ to $n=1$?

    (A) 3

    (B) 6

    (C) 4

    (D) 10

74. If the first orbit radius for $Z=11$ is $r$, then for $Z=1$ it will be:

    (A) $11 r$

    (B) $r/11$

    (C) $121 r$

    (D) $r$

75. The theory that angular momentum $L$ is quantized was given by:

    (A) Bohr

    (B) Rutherford

    (C) Einstein

    (D) de-Broglie

76. $H_\beta$ line is obtained during the transition:

    (A) $n=4 \rightarrow n=2$

    (B) $n=3 \rightarrow n=2$

    (C) $n=2 \rightarrow n=1$

    (D) $n=5 \rightarrow n=2$

77. Which particle must be present in the nucleus of an atom? [BSEB, 2016 (A)]

    (A) Proton

    (B) Neutron

    (C) Electron

    (D) Positron

78. Electron-volt is NOT a unit of:

    (A) Potential difference

    (B) Energy

    (C) Work function

    (D) Ionization energy

79. The velocity of an electron in the second orbit of H-atom compared to the first orbit is:

    (A) Half

    (B) Double

    (C) One-fourth

    (D) Same

80. The relation between Bohr radius $r_n$ and $Z$ is:

    (A) $r_n \propto 1/Z$

    (B) $r_n \propto Z$

    (C) $r_n \propto Z^2$

    (D) $r_n \propto 1/Z^2$

81. The ionization energy of an atom is proportional to:

    (A) $Z^2$

    (B) $1/Z^2$

    (C) $Z$

    (D) $1/Z$

82. The intensity (brightness) of spectral lines depends on:

    (A) Number of electrons

    (B) Mass of the atom

    (C) Temperature

    (D) Both (A) and (C)

83. The energy of transition $n=2$ to $n=1$ for $He^+$ will be:

    (A) $10.2$ eV

    (B) $40.8$ eV

    (C) $13.6$ eV

    (D) $54.4$ eV

84. What was the main drawback of Bohr’s model?

    (A) It was only for single-electron atoms

    (B) It assumed orbits to be circular

    (C) It did not follow Heisenberg’s principle

    (D) All of the above

85. Who discovered X-rays? [BSEB, 2015 (A)]

    (A) Roentgen

    (B) Curie

    (C) Rutherford

    (D) Chadwick

86. The value of specific charge ($e/m$) of an electron is: [BSEB, 2019 (A)]

    (A) $1.76 \times 10^{11}$ C/kg

    (B) $1.76 \times 10^{-11}$ C/kg

    (C) $1.9 \times 10^{-19}$ C/kg

    (D) $1.6 \times 10^{-19}$ C/kg

87. The energy of the photon emitted during transition $n=2$ to $n=1$ is:

    (A) $10.2$ eV

    (B) $12.1$ eV

    (C) $3.4$ eV

    (D) $13.6$ eV

88. The dimensional formula of Rydberg constant is same as that of:

    (A) Wave number

    (B) Frequency

    (C) Velocity

    (D) Momentum

89. The momentum of an electron in the first Bohr orbit of H-atom is:

    (A) $h/2\pi r$

    (B) $h/\pi r$

    (C) $2h/\pi r$

    (D) $h/r$

90. Total energy $E$ of an electron is related to its kinetic energy $K$ as:

    (A) $E = -K$

    (B) $E = U/2$

    (C) Both (A) and (B)

    (D) None of these

91. The energy of Hydrogen atom in excited state $n=3$ is: [BSEB, 2022 (A)]

    (A) $-1.51$ eV

    (B) $-3.4$ eV

    (C) $-13.6$ eV

    (D) $-0.85$ eV

92. Moseley’s Law ($\sqrt{\nu} \propto Z$) is related to:

    (A) X-rays

    (B) $\alpha$-particles

    (C) Spectral series

    (D) Photoelectric effect

93. In the Hydrogen spectrum series, which has the shortest wavelength?

    (A) Lyman series limit

    (B) Balmer series limit

    (C) Paschen series limit

    (D) Brackett series limit

94. 1 Å (Angstrom) is equal to: [BSEB, 2020 (A)]

    (A) $10^{-10}$ m

    (B) $10^{-8}$ cm

    (C) Both (A) and (B)

    (D) $10^{-15}$ m

95. Properties of LASER rays include: [BSEB, 2023 (A)]

    (A) Monochromatic

    (B) Highly directional

    (C) High coherence

    (D) All of the above

96. Energy $E_n$ of the $n^{th}$ orbit according to Bohr’s model $\propto$: [BSEB, 2021 (A)]

    (A) $1/n^2$

    (B) $n^2$

    (C) $1/n$

    (D) $n$

97. The ground state energy of H-atom is $-13.6$ eV. The kinetic energy in this state is:

    (A) $+13.6$ eV

    (B) $-13.6$ eV

    (C) $27.2$ eV

    (D) $0$ eV

98. The angular momentum of an electron for the $L$-shell ($n=2$) is:

    (A) $h/2\pi$

    (B) $h/\pi$

    (C) $3h/2\pi$

    (D) $2h/\pi$

99. The volume of an atom is approximately how many times the volume of its nucleus?

    (A) $10^{15}$ times

    (B) $10^{12}$ times

    (C) $10^5$ times

    (D) $10^3$ times

100. The second line of the Hydrogen spectrum ($H_\beta$) lies in which series?

     (A) Lyman

     (B) Balmer

     (C) Paschen

     (D) Pfund