{"id":12652,"date":"2025-09-20T05:50:41","date_gmt":"2025-09-20T04:50:41","guid":{"rendered":"https:\/\/mcqsadda.com\/?p=12652"},"modified":"2025-10-22T09:55:26","modified_gmt":"2025-10-22T08:55:26","slug":"atomic-and-nuclear-physics-top-100-mcqs-with-answer-and-explanation","status":"publish","type":"post","link":"https:\/\/mcqsadda.com\/index.php\/2025\/09\/20\/atomic-and-nuclear-physics-top-100-mcqs-with-answer-and-explanation\/","title":{"rendered":"Atomic and nuclear physics Top 100 MCQs With Answer and Explanation"},"content":{"rendered":"\n

1. Who proposed the \u201cplum pudding model\u201d of the atom?<\/mark><\/strong>
a) Rutherford
b) Thomson
c) Bohr
d) Dalton
Answer:<\/strong> b
Explanation:<\/strong> J.J. Thomson proposed that the atom is a sphere of positive charge with electrons embedded like plums in pudding.<\/p>\n\n\n\n

2. Rutherford\u2019s scattering experiment demonstrated the existence of:<\/mark><\/strong>
a) Electrons
b) Protons
c) Nucleus
d) Neutrons
Answer:<\/strong> c
Explanation:<\/strong> Alpha particle scattering showed that atoms have a small, dense, positively charged nucleus.<\/p>\n\n\n\n

3. The charge of an electron is:<\/mark><\/strong>
a) C
b) C
c) C
d) C
Answer:<\/strong> b
Explanation:<\/strong> The elementary charge of an electron is negative.<\/p>\n\n\n\n

4. The mass of a proton is approximately:<\/mark><\/strong>
a) Equal to electron mass
b) 1836 times electron mass
c) Half of neutron mass
d) Zero
Answer:<\/strong> b
Explanation:<\/strong> Proton mass \u2248 1836 times electron mass.<\/p>\n\n\n\n

5. Who discovered the neutron?<\/mark><\/strong>
a) Rutherford
b) J.J. Thomson
c) James Chadwick
d) Bohr
Answer:<\/strong> c
Explanation:<\/strong> Chadwick discovered the neutron in 1932.<\/p>\n\n\n\n

6. The nucleus consists of:<\/mark><\/strong>
a) Electrons only
b) Protons only
c) Protons and neutrons
d) Protons and electrons
Answer:<\/strong> c
Explanation:<\/strong> The nucleus contains nucleons (protons and neutrons).<\/p>\n\n\n\n

7. Atomic number is defined as:<\/mark><\/strong>
a) Number of neutrons
b) Number of protons
c) Number of nucleons
d) Mass number
Answer:<\/strong> b
Explanation:<\/strong> Atomic number = number of protons = number of electrons in neutral atom.<\/p>\n\n\n\n

8. Isotopes are atoms having same:<\/mark><\/strong>
a) Mass number but different atomic number
b) Atomic number but different mass number
c) Both mass and atomic number same
d) None
Answer:<\/strong> b
Explanation:<\/strong> Isotopes differ in neutron number but have same proton number.<\/p>\n\n\n\n

9. Isobars are atoms having:<\/mark><\/strong>
a) Same atomic number
b) Same mass number
c) Same neutron number
d) Same electrons
Answer:<\/strong> b
Explanation:<\/strong> Isobars = same mass number, different atomic number.<\/p>\n\n\n\n

10. The nucleus is held together by:<\/mark><\/strong>
a) Gravitational force
b) Electrostatic force
c) Strong nuclear force
d) Magnetic force
Answer:<\/strong> c
Explanation:<\/strong> Strong nuclear force binds protons and neutrons in nucleus.<\/p>\n\n\n\n

11. Who proposed the planetary model of the atom?<\/mark><\/strong>
a) Bohr
b) Rutherford
c) J.J. Thomson
d) Einstein
Answer:<\/strong> b
Explanation:<\/strong> Rutherford proposed electrons revolve around nucleus like planets.<\/p>\n\n\n\n

12. The radius of nucleus is proportional to:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> a
Explanation:<\/strong> Nuclear radius .<\/p>\n\n\n\n

13. The unit of atomic mass (u) is defined as:<\/mark><\/strong>
a) Mass of 1 electron
b) Mass of 1 hydrogen atom
c) 1\/12th mass of C-12 atom
d) Mass of 1 neutron
Answer:<\/strong> c
Explanation:<\/strong> 1 u = 1\/12 mass of carbon-12 atom.<\/p>\n\n\n\n

14. Mass number of an atom is:<\/mark><\/strong>
a) Protons + neutrons
b) Protons + electrons
c) Neutrons + electrons
d) Protons only
Answer:<\/strong> a
Explanation:<\/strong> Mass number = nucleons = protons + neutrons.<\/p>\n\n\n\n

15. Which particle is not a constituent of nucleus?<\/mark><\/strong>
a) Proton
b) Neutron
c) Electron
d) None
Answer:<\/strong> c
Explanation:<\/strong> Electrons revolve outside nucleus.<\/p>\n\n\n\n

16. Energy levels in an atom are:<\/mark><\/strong>
a) Continuous
b) Discrete
c) Random
d) Infinite
Answer:<\/strong> b
Explanation:<\/strong> Electrons occupy discrete quantized energy levels.<\/p>\n\n\n\n

17. The maximum number of electrons in an orbit is given by:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> b
Explanation:<\/strong> Maximum electrons in nth shell = .<\/p>\n\n\n\n

18. The first shell (K-shell) can have maximum electrons:<\/mark><\/strong>
a) 2
b) 8
c) 18
d) 32
Answer:<\/strong> a
Explanation:<\/strong> For , max = .<\/p>\n\n\n\n

19. The discovery of discrete atomic spectra supported which theory?<\/mark><\/strong>
a) Classical mechanics
b) Bohr\u2019s quantization
c) Thomson\u2019s model
d) Rutherford\u2019s model
Answer:<\/strong> b
Explanation:<\/strong> Discrete spectra are explained by Bohr\u2019s quantization of orbits.<\/p>\n\n\n\n

20. In Rutherford scattering, most alpha particles passed undeflected because:<\/mark><\/strong>
a) Nucleus is heavy
b) Atom is mostly empty space
c) Electrons are very small
d) Speed was high
Answer:<\/strong> b
Explanation:<\/strong> Most of atom\u2019s volume is empty space.<\/p>\n\n\n\n

21. In hydrogen atom, electron revolves around nucleus due to<\/mark><\/strong>:
a) Gravitational force
b) Magnetic force
c) Electrostatic attraction
d) Nuclear force
Answer:<\/strong> c
Explanation:<\/strong> Coulomb force acts between proton and electron.<\/p>\n\n\n\n

22. In Bohr\u2019s model, angular momentum of electron is:<\/mark><\/strong>
a) Quantized
b) Continuous
c) Zero
d) Infinite
Answer:<\/strong> a
Explanation:<\/strong> Angular momentum = .<\/p>\n\n\n\n

23. Which emission occurs when an electron jumps from higher to lower orbit?<\/mark><\/strong>
a) Absorption
b) Radiation of photon
c) Scattering
d) Nuclear reaction
Answer:<\/strong> b
Explanation:<\/strong> Photon of energy equal to difference in levels is emitted.<\/p>\n\n\n\n

24. The order of magnitude of atomic radius is:<\/mark><\/strong>
a) m
b) m
c) m
d) m
Answer:<\/strong> a
Explanation:<\/strong> Atomic radius \u2248 \u00c5 = m.<\/p>\n\n\n\n

25. The order of magnitude of nuclear radius is:<\/mark><\/strong>
a) m
b) m
c) m
d) m
Answer:<\/strong> c
Explanation:<\/strong> Nuclear radius \u2248 fermi = to m.<\/p>\n\n\n\n

26. The four quantum numbers completely describe:<\/mark><\/strong>
a) Nucleus
b) Electron in an atom
c) Proton in nucleus
d) Neutron in nucleus
Answer:<\/strong> b
Explanation:<\/strong> Principal, azimuthal, magnetic, and spin quantum numbers specify the state of an electron in an atom.<\/p>\n\n\n\n

27. Principal quantum number (n) indicates:<\/mark><\/strong>
a) Shape of orbital
b) Orientation of orbital
c) Energy level\/shell
d) Spin of electron
Answer:<\/strong> c
Explanation:<\/strong> specifies main shell and energy level of electron.<\/p>\n\n\n\n

28. Azimuthal (angular momentum) quantum number (l) gives:<\/mark><\/strong>
a) Size of orbital
b) Shape of orbital
c) Orientation
d) Spin
Answer:<\/strong> b
Explanation:<\/strong> defines shape: .<\/p>\n\n\n\n

29. For , possible values of are:<\/mark><\/strong>
a) 0, 1, 2
b) 1, 2, 3
c) 0, 2, 3
d) 1, 3
Answer:<\/strong> a
Explanation:<\/strong> ranges from 0 to . For , .<\/p>\n\n\n\n

30. Magnetic quantum number () defines:<\/mark><\/strong>
a) Energy of electron
b) Shape of orbital
c) Orientation of orbital
d) Spin
Answer:<\/strong> c
Explanation:<\/strong> specifies orientation in space.<\/p>\n\n\n\n

31. Spin quantum number () can have values:<\/mark><\/strong>
a) 0, 1, 2
b) +1, -1
c) +1\/2, -1\/2
d) +1\/3, -1\/3
Answer:<\/strong> c
Explanation:<\/strong> Electron spin is intrinsic angular momentum with \u00b11\/2 values.<\/p>\n\n\n\n

32. The maximum number of electrons in a subshell is:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> b
Explanation:<\/strong> Each orbital can hold 2 electrons; number of orbitals in subshell = .<\/p>\n\n\n\n

33. Which series of hydrogen spectrum lies in visible region?<\/mark><\/strong>
a) Lyman
b) Balmer
c) Paschen
d) Brackett
Answer:<\/strong> b
Explanation:<\/strong> Balmer series (transitions to ) appears in visible spectrum.<\/p>\n\n\n\n

34. The Lyman series of hydrogen spectrum lies in:<\/mark><\/strong>
a) Visible
b) Infrared
c) Ultraviolet
d) Microwave
Answer:<\/strong> c
Explanation:<\/strong> Lyman series (transitions to ) lies in UV region.<\/p>\n\n\n\n

35. The Paschen series belongs to:<\/mark><\/strong>
a) Visible region
b) Infrared region
c) Ultraviolet region
d) X-ray region
Answer:<\/strong> b
Explanation:<\/strong> Paschen series (transitions to ) lies in infrared.<\/p>\n\n\n\n

36. The energy of a photon is given by:<\/mark><\/strong>
a)
b)
c)
d) Both b and c
Answer:<\/strong> d
Explanation:<\/strong> Photon energy can be expressed using frequency or wavelength.<\/p>\n\n\n\n

37. In Bohr\u2019s model, energy of electron in nth orbit is proportional to:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> b
Explanation:<\/strong> .<\/p>\n\n\n\n

38. Rydberg constant is used to calculate:<\/mark><\/strong>
a) Mass defect
b) Atomic radius
c) Wavelengths of hydrogen spectral lines
d) Nuclear charge
Answer:<\/strong> c
Explanation:<\/strong> Rydberg formula gives wavelengths of hydrogen spectrum.<\/p>\n\n\n\n

39. Moseley\u2019s law relates:<\/mark><\/strong>
a) Frequency of X-rays and atomic number
b) Energy levels and radius
c) Mass number and charge
d) Neutrons and stability
Answer:<\/strong> a
Explanation:<\/strong> . Shows atomic number determines X-ray frequency.<\/p>\n\n\n\n

40. Who discovered X-rays?<\/mark><\/strong>
a) Roentgen
b) Rutherford
c) Planck
d) Einstein
Answer:<\/strong> a
Explanation:<\/strong> Wilhelm Roentgen discovered X-rays in 1895.<\/p>\n\n\n\n

41. X-rays are produced when:<\/mark><\/strong>
a) Electrons collide with nucleus
b) Electrons accelerate across vacuum tube and hit metal target
c) Protons combine with neutrons
d) Gamma decay occurs
Answer:<\/strong> b
Explanation:<\/strong> Sudden deceleration of electrons produces X-rays.<\/p>\n\n\n\n

42. The minimum wavelength of X-rays depends on:<\/mark><\/strong>
a) Target material
b) Accelerating voltage
c) Electron mass
d) Current
Answer:<\/strong> b
Explanation:<\/strong> .<\/p>\n\n\n\n

43. Characteristic X-rays are emitted when:<\/mark><\/strong>
a) Electron jumps from one shell to another
b) Atom undergoes radioactive decay
c) Proton leaves nucleus
d) Nucleus fissions
Answer:<\/strong> a
Explanation:<\/strong> Characteristic X-rays arise due to electronic transitions in inner shells.<\/p>\n\n\n\n

44. Continuous X-ray spectrum is due to:<\/mark><\/strong>
a) Braking radiation (Bremsstrahlung)
b) Nuclear reaction
c) Photon scattering
d) Photoelectric effect
Answer:<\/strong> a
Explanation:<\/strong> Bremsstrahlung radiation occurs due to deceleration of electrons.<\/p>\n\n\n\n

45. Which of the following is not a property of X-rays?<\/mark><\/strong>
a) Electrically charged
b) High penetrating power
c) Travel in straight lines
d) Cause fluorescence
Answer:<\/strong> a
Explanation:<\/strong> X-rays are neutral electromagnetic waves.<\/p>\n\n\n\n

46. The energy of an X-ray photon of wavelength 1 \u00c5 is approximately:<\/mark><\/strong>
a) 1.24 keV
b) 12.4 keV
c) 124 keV
d) 1240 keV
Answer:<\/strong> b
Explanation:<\/strong> keV.<\/p>\n\n\n\n

47. The diffraction of X-rays is explained by:<\/mark><\/strong>
a) Davisson\u2013Germer experiment
b) Bragg\u2019s law
c) Rutherford experiment
d) Photoelectric effect
Answer:<\/strong> b
Explanation:<\/strong> Bragg\u2019s law: .<\/p>\n\n\n\n

48. X-rays are used in:<\/mark><\/strong>
a) Medical imaging
b) Crystal structure analysis
c) Cancer treatment
d) All of these
Answer:<\/strong> d
Explanation:<\/strong> X-rays are widely used in medicine and material science.<\/p>\n\n\n\n

49. The wavelength of visible light is of the order of:<\/mark><\/strong>
a) 1 \u00c5
b) 100 \u00c5
c) 5000 \u00c5
d) 10\u2075 \u00c5
Answer:<\/strong> c
Explanation:<\/strong> Visible spectrum ranges from 4000\u20137000 \u00c5.<\/p>\n\n\n\n

50. Compared to visible light, X-rays have:<\/mark><\/strong>
a) Longer wavelength
b) Shorter wavelength
c) Equal wavelength
d) Infinite wavelength
Answer:<\/strong> b
Explanation:<\/strong> X-rays have wavelength 0.01\u201310 \u00c5, shorter than visible light.<\/p>\n\n\n\n

51. Radioactivity was discovered by:<\/mark><\/strong>
a) Rutherford
b) Becquerel
c) Curie
d) Thomson
Answer:<\/strong> b
Explanation:<\/strong> Henri Becquerel discovered natural radioactivity in 1896 while studying uranium salts.<\/p>\n\n\n\n

52. The type of radiation with highest penetrating power is:<\/mark><\/strong>
a) Alpha
b) Beta
c) Gamma
d) X-ray
Answer:<\/strong> c
Explanation:<\/strong> Gamma rays are highly penetrating electromagnetic radiation.<\/p>\n\n\n\n

53. Alpha particles are:<\/mark><\/strong>
a) Electrons
b) Helium nuclei
c) Neutrons
d) Photons
Answer:<\/strong> b
Explanation:<\/strong> Alpha = 2 protons + 2 neutrons (He nucleus).<\/p>\n\n\n\n

54. Beta particles are<\/mark><\/strong>:
a) Electrons
b) Protons
c) Helium nuclei
d) Neutrons
Answer:<\/strong> a
Explanation:<\/strong> Beta radiation consists of high-speed electrons (or positrons).<\/p>\n\n\n\n

55. The half-life of a radioactive substance is<\/mark><\/strong>:
a) Time taken for all nuclei to decay
b) Time taken for half of nuclei to decay
c) Time taken for energy to reduce to half
d) Time for complete disintegration
Answer:<\/strong> b
Explanation:<\/strong> Half-life = time for 50% of radioactive nuclei to decay.<\/p>\n\n\n\n

56. The decay constant is related to half-life by:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> b
Explanation:<\/strong> .<\/p>\n\n\n\n

57. In alpha decay, the mass number decreases by:
<\/mark><\/strong>a) 1
b) 2
c) 4
d) 0
Answer:<\/strong> c
Explanation:<\/strong> Alpha particle = 4 nucleons, so mass number decreases by 4.<\/p>\n\n\n\n

58. In beta minus decay:<\/mark><\/strong>
a) Proton \u2192 neutron + positron
b) Neutron \u2192 proton + electron
c) Neutron \u2192 proton + alpha
d) Proton \u2192 neutron + gamma
Answer:<\/strong> b
Explanation:<\/strong> Beta minus decay: n \u2192 p + e\u207b + antineutrino.<\/p>\n\n\n\n

59. Gamma decay changes:<\/mark><\/strong>
a) Atomic number only
b) Mass number only
c) Both atomic and mass number
d) Energy state only
Answer:<\/strong> d
Explanation:<\/strong> Gamma emission lowers energy of nucleus without changing A or Z.<\/p>\n\n\n\n

60. The unit of radioactivity is:<\/mark><\/strong>
a) Coulomb
b) Becquerel
c) Curie
d) Both b and c
Answer:<\/strong> d
Explanation:<\/strong> 1 Bq = 1 decay\/sec; 1 Ci = decays\/sec.<\/p>\n\n\n\n

61. Spontaneous fission occurs in:<\/mark><\/strong>
a) Light nuclei
b) Heavy nuclei
c) Hydrogen
d) Alpha particle
Answer:<\/strong> b
Explanation:<\/strong> Heavy nuclei (like U-235) can undergo spontaneous fission.<\/p>\n\n\n\n

62. The law governing radioactive decay is:<\/mark><\/strong>
a) Newton\u2019s law
b) Exponential decay law
c) Coulomb\u2019s law
d) Boyle\u2019s law
Answer:<\/strong> b
Explanation:<\/strong> Number of undecayed nuclei decreases exponentially: .<\/p>\n\n\n\n

63. Mass defect is:<\/mark><\/strong>
a) Extra mass of nucleus
b) Difference between sum of nucleon masses and actual mass of nucleus
c) Electron mass
d) Proton mass
Answer:<\/strong> b
Explanation:<\/strong> Mass defect = .<\/p>\n\n\n\n

64. Binding energy of nucleus is:<\/mark><\/strong>
a) Energy needed to remove all electrons
b) Energy released when nucleus forms from nucleons
c) Kinetic energy of nucleons
d) Energy of alpha decay
Answer:<\/strong> b
Explanation:<\/strong> Binding energy = energy released in forming nucleus from nucleons.<\/p>\n\n\n\n

65. The nucleus with maximum binding energy per nucleon is:<\/mark><\/strong>
a) Hydrogen
b) Iron
c) Uranium
d) Helium
Answer:<\/strong> b
Explanation:<\/strong> Iron-56 has highest stability.<\/p>\n\n\n\n

66. The neutron-to-proton ratio for stable nuclei increases with:<\/mark><\/strong>
a) Atomic mass
b) Atomic number
c) Electron number
d) Alpha particles
Answer:<\/strong> b
Explanation:<\/strong> Heavier nuclei need more neutrons to overcome proton-proton repulsion.<\/p>\n\n\n\n

67. The nucleus of an alpha particle has:<\/mark><\/strong>
a) 2 protons, 1 neutron
b) 2 protons, 2 neutrons
c) 1 proton, 1 neutron
d) 1 proton only
Answer:<\/strong> b
Explanation:<\/strong> Alpha = He nucleus = 2p + 2n.<\/p>\n\n\n\n

68. The neutrino was proposed to:<\/mark><\/strong>
a) Balance charge in beta decay
b) Explain energy conservation in beta decay
c) Explain mass defect
d) Explain gamma decay
Answer:<\/strong> b
Explanation:<\/strong> Pauli proposed neutrino to conserve energy and momentum in beta decay.<\/p>\n\n\n\n

69. Beta plus decay emits:<\/mark><\/strong>
a) Electron
b) Positron
c) Alpha particle
d) Gamma ray
Answer:<\/strong> b
Explanation:<\/strong> \u03b2\u207a decay: proton \u2192 neutron + positron + neutrino.<\/p>\n\n\n\n

70. Natural radioactivity was first observed in:<\/mark><\/strong>
a) Uranium
b) Thorium
c) Radium
d) Polonium
Answer:<\/strong> a
Explanation:<\/strong> Becquerel observed uranium emitting radiation spontaneously.<\/p>\n\n\n\n

71. Artificial radioactivity was first produced by:<\/mark><\/strong>
a) Rutherford
b) Joliot-Curie
c) Chadwick
d) Bohr
Answer:<\/strong> b
Explanation:<\/strong> Joliot-Curie bombarded Al with alpha particles, producing radioactive P.<\/p>\n\n\n\n

72. Geiger-M\u00fcller counter detects:<\/mark><\/strong>
a) Neutrons
b) Alpha, beta, gamma radiation
c) X-rays only
d) Protons only
Answer:<\/strong> b
Explanation:<\/strong> GM counter detects ionizing radiation (\u03b1, \u03b2, \u03b3).<\/p>\n\n\n\n

73. Scintillation counter works on:<\/mark><\/strong>
a) Photoelectric effect
b) Ionization
c) Fluorescence
d) Bremsstrahlung
Answer:<\/strong> c
Explanation:<\/strong> Radiation produces flashes of light in scintillator crystal.<\/p>\n\n\n\n

74. The Curie (Ci) is equal to:<\/mark><\/strong>
a) decays\/sec
b) decays\/sec
c) decays\/sec
d) decays\/sec
Answer:<\/strong> a
Explanation:<\/strong> 1 Ci = Bq.<\/p>\n\n\n\n

75. In nuclear stability, magic numbers are:<\/mark><\/strong>
a) 2, 8, 20, 28, 50, 82, 126
b) 1, 2, 3, 4, 5
c) 10, 20, 30, 40
d) None
Answer:<\/strong> a
Explanation:<\/strong> Nuclei with magic numbers of protons or neutrons are especially stable.<\/p>\n\n\n\n

76. Nuclear fission was first discovered by:<\/mark><\/strong>
a) Rutherford
b) Fermi
c) Hahn and Strassmann
d) Bohr
Answer:<\/strong> c
Explanation:<\/strong> Otto Hahn and Fritz Strassmann discovered nuclear fission in 1938 by bombarding uranium with neutrons.<\/p>\n\n\n\n

77. In fission of U-235, which particle initiates the chain reaction?<\/mark><\/strong>
a) Proton
b) Electron
c) Neutron
d) Alpha particle
Answer:<\/strong> c
Explanation:<\/strong> A neutron initiates fission by splitting the nucleus.<\/p>\n\n\n\n

78. In nuclear fusion, energy is released due to:<\/mark><\/strong>
a) Mass increase
b) Mass defect
c) Electron capture
d) Beta decay
Answer:<\/strong> b
Explanation:<\/strong> Fusion releases energy because mass of final nucleus < sum of masses of reactants.<\/p>\n\n\n\n

79. Fusion occurs in:<\/mark><\/strong>
a) Uranium reactors
b) Sun and stars
c) Coal plants
d) Batteries
Answer:<\/strong> b
Explanation:<\/strong> Sun produces energy via hydrogen fusion.<\/p>\n\n\n\n

80. Critical mass is:<\/mark><\/strong>
a) Minimum mass of fuel for fission chain reaction
b) Maximum mass allowed in reactor
c) Mass of neutron
d) Mass of alpha particle
Answer:<\/strong> a
Explanation:<\/strong> Critical mass is necessary for sustained chain reaction.<\/p>\n\n\n\n

81. Energy released in fission of 1 kg of U-235 is approximately:<\/mark><\/strong>
a) J
b) J
c) J
d) J
Answer:<\/strong> a
Explanation:<\/strong> Fission of 1 kg U-235 releases ~\u00a0J.<\/p>\n\n\n\n

82. Chain reaction is controlled in nuclear reactors using:<\/mark><\/strong>
a) Control rods
b) Moderator
c) Coolant
d) Reflector
Answer:<\/strong> a
Explanation:<\/strong> Control rods absorb excess neutrons to regulate reaction.<\/p>\n\n\n\n

83. The moderator in a nuclear reactor is used to:<\/mark><\/strong>
a) Slow down neutrons
b) Absorb gamma rays
c) Cool fuel
d) Increase fission rate
Answer:<\/strong> a
Explanation:<\/strong> Slow neutrons are more effective in causing fission; moderator (e.g., heavy water, graphite) slows them.<\/p>\n\n\n\n

84. Thermal neutrons have energy of about:<\/mark><\/strong>
a) 0.025 eV
b) 1 eV
c) 100 eV
d) 1 keV
Answer:<\/strong> a
Explanation:<\/strong> Thermal neutrons = slow neutrons in thermal equilibrium at room temperature.<\/p>\n\n\n\n

85. Breeder reactors produce:<\/mark><\/strong>
a) Electricity directly
b) More fissile material than consumed
c) Neutrons
d) Heavy water
Answer:<\/strong> b
Explanation:<\/strong> Breeder reactors convert fertile U-238 or Th-232 into fissile Pu-239 or U-233.<\/p>\n\n\n\n

86. The energy produced per nucleon in fusion is:<\/mark><\/strong>
a) Maximum for hydrogen
b) Maximum for iron
c) Minimum for hydrogen
d) Same for all elements
Answer:<\/strong> b
Explanation:<\/strong> Binding energy per nucleon is maximum for iron; fusion of light nuclei releases energy.<\/p>\n\n\n\n

87. Which isotope is used as fuel in nuclear fusion?<\/mark><\/strong>
a) Uranium-235
b) Deuterium and Tritium
c) Plutonium-239
d) Thorium-232
Answer:<\/strong> b
Explanation:<\/strong> Fusion experiments use D + T reactions.<\/p>\n\n\n\n

88. The first nuclear reactor (Chicago Pile-1) was built by:<\/mark><\/strong>
a) Fermi
b) Rutherford
c) Bohr
d) Chadwick
Answer:<\/strong> a
Explanation:<\/strong> Enrico Fermi built first controlled nuclear reactor in 1942.<\/p>\n\n\n\n

89. Half-life of U-238 is approximately:<\/mark><\/strong>
a) 4.5 \u00d7 10\u2079 years
b) 7.1 \u00d7 10\u2078 years
c) 1.3 \u00d7 10\u2079 years
d) 2 \u00d7 10\u2076 years
Answer:<\/strong> a
Explanation:<\/strong> U-238 has very long half-life \u2248 age of Earth.<\/p>\n\n\n\n

90. A positron is:<\/mark><\/strong>
a) Electron
b) Proton
c) Anti-electron
d) Neutron
Answer:<\/strong> c
Explanation:<\/strong> Positron = antiparticle of electron (+1 charge).<\/p>\n\n\n\n

91. Electron capture involves:<\/mark><\/strong>
a) Neutron \u2192 proton
b) Proton \u2192 neutron by capturing orbital electron
c) Emission of beta particle
d) Emission of alpha particle
Answer:<\/strong> b
Explanation:<\/strong> Proton captures inner electron, transforms to neutron, emitting neutrino.<\/p>\n\n\n\n

92. In alpha decay, element shifts:<\/mark><\/strong>
a) One place left in periodic table
b) Two places left
c) One place right
d) Two places right
Answer:<\/strong> b
Explanation:<\/strong> Atomic number decreases by 2 (Z\u2192Z-2) in \u03b1-decay.<\/p>\n\n\n\n

93. Mass-energy equivalence is given by:<\/mark><\/strong>
a)
b)
c)
d)
Answer:<\/strong> b
Explanation:<\/strong> Einstein\u2019s formula relates mass and energy.<\/p>\n\n\n\n

94. Fission fragments are:<\/mark><\/strong>
a) Stable nuclei
b) Neutrons only
c) Highly radioactive nuclei
d) Alpha particles
Answer:<\/strong> c
Explanation:<\/strong> Fission products are neutron-rich, highly radioactive nuclei.<\/p>\n\n\n\n

95. Energy of gamma photon emitted in nuclear decay is:<\/mark><\/strong>
a) Kinetic energy of nucleus
b) Binding energy of nucleon
c) Energy difference between nuclear states
d) Mass defect
Answer:<\/strong> c
Explanation:<\/strong> Gamma emission corresponds to nuclear de-excitation.<\/p>\n\n\n\n

96. Fusion reaction in Sun converts:<\/mark><\/strong>
a) Hydrogen \u2192 Helium
b) Helium \u2192 Carbon
c) Oxygen \u2192 Nitrogen
d) Uranium \u2192 Lead
Answer:<\/strong> a
Explanation:<\/strong> Proton-proton chain converts hydrogen into helium in stars.<\/p>\n\n\n\n

97. Nuclear reactions are generally:<\/mark><\/strong>
a) Exothermic for heavy nuclei fission
b) Endothermic for light nuclei fusion
c) Exothermic for both light nuclei fusion and heavy nuclei fission
d) Endothermic for heavy nuclei fission
Answer:<\/strong> c
Explanation:<\/strong> Both fission (heavy) and fusion (light) release energy.<\/p>\n\n\n\n

98. Radioisotopes used in medicine are called:<\/mark><\/strong>
a) Tracers
b) Catalysts
c) Moderators
d) Fuel
Answer:<\/strong> a
Explanation:<\/strong> Radioactive isotopes trace metabolic pathways or treat diseases.<\/p>\n\n\n\n

99. Half-life is independent of:<\/mark><\/strong>
a) Temperature
b) Pressure
c) Chemical combination
d) All of the above
Answer:<\/strong> d
Explanation:<\/strong> Radioactive decay is nuclear; chemical\/physical conditions do not affect it.<\/p>\n\n\n\n

100. Nuclear energy is safer than fossil fuels because:<\/mark><\/strong>
a) No radiation
b) No greenhouse gas emission
c) Unlimited fuel
d) Cheap
Answer:<\/strong> b
Explanation:<\/strong> Nuclear power releases no CO\u2082, though radioactive waste must be managed.<\/p>\n","protected":false},"excerpt":{"rendered":"

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