1. Who discovered nuclear fission?
a) Hahn & Strassmann
b) Einstein
c) Rutherford
d) Curie
Answer: a
Explanation: Otto Hahn and Fritz Strassmann (1938) discovered splitting of U-235 by neutrons.
2. Nuclear fission occurs when:
a) Heavy nucleus splits into smaller nuclei
b) Small nuclei combine
c) Atom ionizes
d) Proton decays
Answer: a
Explanation: Fission releases energy due to mass defect.
3. The first controlled nuclear chain reaction was by:
a) Enrico Fermi
b) Rutherford
c) Einstein
d) Bohr
Answer: a
Explanation: Fermi (1942) achieved controlled fission in Chicago Pile-1.
4. Nuclear fission releases energy because:
a) Mass of products < mass of reactants
b) Mass increases
c) No mass change
d) Proton decays
Answer: a
Explanation: Mass defect converts to energy via 
.
5. Fission is induced by:
a) Neutron absorption
b) Proton absorption
c) Electron capture
d) Gamma rays only
Answer: a
Explanation: Thermal neutrons induce fission in U-235.
6. Fission of U-235 by thermal neutron produces:
a) Two fission fragments + neutrons + energy
b) Only energy
c) Only neutrons
d) Alpha particles
Answer: a
Explanation: Typical fission releases ~200 MeV energy.
7. Typical energy released in fission of 1 U-235 nucleus:
a) ~200 MeV
b) 1 MeV
c) 10 MeV
d) 1 GeV
Answer: a
Explanation: Energy comes from mass defect of nucleus.
8. Heavy elements that can undergo fission:
a) U-235, Pu-239
b) H-1, H-2
c) He-4, Li-6
d) C-12
Answer: a
Explanation: Only heavy, fissile isotopes split easily with neutrons.
9. Fission fragments are usually:
a) Radioactive
b) Stable
c) Neutral
d) Alpha particles
Answer: a
Explanation: Fission products like Sr-90, Cs-137 are radioactive.
10. Average number of neutrons released per fission of U-235:
a) 2–3
b) 1
c) 5
d) 0
Answer: a
Explanation: These neutrons can sustain chain reaction.
11. Spontaneous fission occurs:
a) Without external neutron
b) Only with neutron
c) Only with gamma
d) Never
Answer: a
Explanation: Some heavy nuclei (e.g., Cf-252) fission spontaneously.
12. Fissile materials:
a) U-235, Pu-239
b) U-238, Th-232
c) He-4
d) Li-7
Answer: a
Explanation: Can sustain chain reaction with thermal neutrons.
13. Fertile materials:
a) U-238, Th-232
b) U-235
c) Pu-239
d) H-2
Answer: a
Explanation: Can convert to fissile isotopes by neutron absorption.
14. Fast neutrons in fission are slowed by:
a) Moderator
b) Control rods
c) Shielding
d) Coolant
Answer: a
Explanation: Materials like water, graphite reduce neutron speed.
15. Mass defect in fission is:
a) Converted to energy
b) Converted to matter
c) Lost
d) Zero
Answer: a
Explanation: Energy released calculated by .
16. First nuclear bomb used:
a) U-235 and Pu-239
b) U-238 only
c) H-2
d) Li-6 only
Answer: a
Explanation: “Little Boy” used U-235; “Fat Man” used Pu-239.
17. Fission reaction can be:
a) Controlled (reactor) or uncontrolled (bomb)
b) Only controlled
c) Only uncontrolled
d) Impossible
Answer: a
Explanation: Rate of neutron multiplication distinguishes reactor and bomb.
18. Critical mass depends on:
a) Material, shape, purity
b) Color
c) Temperature only
d) Pressure only
Answer: a
Explanation: Spherical, pure fissile material lowers critical mass.
19. Supercritical mass means:
a) Chain reaction increases
b) Reaction stops
c) Stable
d) Slow reaction
Answer: a
Explanation: More than critical mass leads to exponential neutron multiplication.
20. Moderator slows neutrons but does not:
a) Absorb neutrons significantly
b) Increase temperature
c) Reflect neutrons
d) Produce fission
Answer: a
Explanation: Slow neutrons enhance fission probability without absorption.
21. Neutron reflector in reactors:
a) Bounces back escaping neutrons
b) Absorbs neutrons
c) Emits gamma rays
d) Produces energy
Answer: a
Explanation: Increases neutron economy and reduces critical mass.
22. Uranium-238 is:
a) Fertile
b) Fissile
c) Stable
d) Radioactive only
Answer: a
Explanation: Absorbs neutron → Pu-239 fissile material.
23. Plutonium-239 is obtained by:
a) Neutron capture in U-238
b) Beta decay of U-235
c) Fusion of H-2
d) Direct extraction from nature
Answer: a
Explanation: 
.
24. Fission product yields:
a) Random nuclei
b) Only alpha particles
c) Only neutrons
d) Only gamma
Answer: a
Explanation: Fission splits nucleus into unequal fragments with neutrons emitted.
25. Fission of U-235 produces most energy as:
a) Kinetic energy of fission fragments
b) Neutrons
c) Gamma only
d) Beta only
Answer: a
Explanation: ~85% energy carried by fragment kinetic energy; rest by neutrons/gamma.
26. Chain reaction occurs when:
a) Neutrons from one fission induce further fissions
b) Protons collide
c) Electrons escape
d) Alpha particles emitted
Answer: a
Explanation: Released neutrons trigger further fissions, sustaining reaction.
27. Controlled chain reaction is used in:
a) Nuclear reactors
b) Bombs
c) Stars
d) Solar cells
Answer: a
Explanation: Neutron population is regulated to release steady energy.
28. Uncontrolled chain reaction is:
a) Nuclear explosion
b) Nuclear power
c) Solar fusion
d) Chemical reaction
Answer: a
Explanation: Rapid multiplication of neutrons causes massive energy release.
29. Moderator in reactor:
a) Slows down neutrons
b) Absorbs neutrons
c) Increases neutron speed
d) Produces energy
Answer: a
Explanation: Slow neutrons are more likely to induce fission in U-235.
30. Examples of moderators:
a) Heavy water, graphite, light water
b) Lead, cadmium
c) Uranium-238
d) Plutonium
Answer: a
Explanation: Non-absorbing substances that slow down neutrons.
31. Control rods absorb:
a) Excess neutrons
b) Energy
c) Heat
d) Protons
Answer: a
Explanation: Made of cadmium, boron, or hafnium to control chain reaction.
32. Coolant in reactor is used to:
a) Remove heat from core
b) Reflect neutrons
c) Produce neutrons
d) Absorb radiation
Answer: a
Explanation: Circulates heat to generate steam for electricity.
33. Fast neutron reactors:
a) Use fast neutrons without moderator
b) Use thermal neutrons
c) Absorb neutrons only
d) Use chemical energy
Answer: a
Explanation: No moderator needed; fuel enriched for fast fission.
34. Breeder reactor converts:
a) Fertile U-238 → Fissile Pu-239
b) Pu-239 → U-238
c) H-2 → He-3
d) None
Answer: a
Explanation: Produces more fissile material than consumed.
35. Criticality means:
a) Chain reaction is self-sustaining
b) Reaction stops
c) Neutrons absorbed completely
d) Mass is stable
Answer: a
Explanation: Number of neutrons causing fissions balances those lost.
36. Subcritical mass:
a) Reaction dies out
b) Reaction increases
c) Reaction steady
d) Explosive
Answer: a
Explanation: Not enough fissile material for chain reaction.
37. Supercritical mass:
a) Reaction accelerates
b) Reaction steady
c) Reaction stops
d) None
Answer: a
Explanation: Mass exceeds critical → exponential increase in fissions.
38. Energy produced per fission of U-235:
a) ~200 MeV
b) 1 MeV
c) 10 MeV
d) 1000 MeV
Answer: a
Explanation: Majority released as kinetic energy of fragments.
39. Neutrons released per fission:
a) 2–3
b) 1
c) 5–6
d) 0
Answer: a
Explanation: These neutrons sustain chain reaction.
40. Thermal neutrons have energy:
a) ~0.025 eV
b) 1 MeV
c) 100 keV
d) 10 MeV
Answer: a
Explanation: Neutrons in equilibrium with room temperature (~25 meV).
41. Fast neutrons have energy:
a) 1–2 MeV
b) 0.025 eV
c) 1 eV
d) 10 meV
Answer: a
Explanation: Produced directly from fission, need slowing by moderator.
42. Uranium enrichment increases:
a) U-235 fraction
b) U-238 fraction
c) Pu-239 fraction
d) None
Answer: a
Explanation: Enrichment increases fissile isotope content for reactor/bomb use.
43. Natural uranium contains:
a) 0.7% U-235, 99.3% U-238
b) 50% U-235
c) 100% U-238
d) 10% Pu-239
Answer: a
Explanation: Low fissile fraction requires enrichment for reactors.
44. Pressurized water reactor (PWR) uses:
a) Water as coolant and moderator
b) Graphite as moderator
c) Heavy water only
d) Air cooling
Answer: a
Explanation: Pressurized water prevents boiling, transfers heat to turbine.
45. Boiling water reactor (BWR):
a) Water boils in core → steam directly drives turbine
b) Uses graphite
c) Uses heavy water
d) No water
Answer: a
Explanation: Steam generated in core goes directly to turbines.
46. CANDU reactor uses:
a) Heavy water moderator and coolant
b) Light water
c) Graphite
d) Gas
Answer: a
Explanation: Uses natural uranium; heavy water enhances neutron economy.
47. Fast breeder reactors produce:
a) More fissile material than consumed
b) Less
c) Equal
d) None
Answer: a
Explanation: Fertile U-238 → Pu-239 conversion.
48. Nuclear reactor safety involves:
a) Control rods, containment, cooling
b) Only shielding
c) Only moderators
d) None
Answer: a
Explanation: Ensures controlled reaction, prevents meltdown, protects environment.
49. Fission produces:
a) Neutrons, gamma, energy, radioactive fragments
b) Only energy
c) Only gamma
d) Only neutrons
Answer: a
Explanation: Multiple products released; fragments radioactive.
50. Nuclear waste is mainly:
a) Fission products
b) Uranium only
c) Water
d) Moderator
Answer: a
Explanation: Radioactive isotopes like Cs-137, Sr-90, Tc-99 are hazardous.
51. Nuclear fusion is the process of:
a) Light nuclei combining to form heavier nucleus
b) Heavy nuclei splitting
c) Electron capture
d) Proton decay
Answer: a
Explanation: Fusion releases energy due to mass defect, opposite of fission.
52. Fusion requires:
a) Extremely high temperature and pressure
b) Low temperature
c) Normal pressure
d) Neutron absorption only
Answer: a
Explanation: Overcomes electrostatic repulsion (Coulomb barrier) between nuclei.
53. Fusion in stars primarily converts:
a) Hydrogen → Helium
b) Uranium → Lead
c) Helium → Hydrogen
d) Carbon → Oxygen
Answer: a
Explanation: Proton-proton chain and CNO cycle fuse H into He, releasing energy.
54. Energy released in fusion comes from:
a) Mass defect → E = Δm c²
b) Neutron absorption
c) Alpha decay
d) Electron capture
Answer: a
Explanation: Mass of product < sum of reactants; energy released as radiation and kinetic energy.
55. Temperature required for fusion of H isotopes:
a) ~10⁷–10⁸ K
b) Room temperature
c) 1000 K
d) 0 K
Answer: a
Explanation: Extreme temperature needed to overcome Coulomb repulsion.
56. Deuterium-deuterium fusion reaction produces:
a) Helium-3 + neutron or tritium + proton
b) Only helium
c) Alpha particle only
d) Neutron only
Answer: a
Explanation: Fusion of D nuclei has two possible branches releasing energy.
57. Deuterium-tritium (D-T) fusion reaction releases:
a) ~17.6 MeV energy
b) 200 MeV
c) 1 MeV
d) 100 MeV
Answer: a
Explanation: Most promising reaction for fusion reactors.
58. Fusion produces more energy per unit mass than fission:
a) True
b) False
Answer: a
Explanation: Energy density of fusion (H → He) is much higher than U-235 fission.
59. Fusion requires confinement:
a) Magnetic or inertial
b) Chemical
c) Thermal only
d) Electric only
Answer: a
Explanation: Plasma must be confined at high temperature for fusion to occur.
60. Stars shine due to:
a) Nuclear fusion in core
b) Fission reactions
c) Chemical reactions
d) Gravitational collapse only
Answer: a
Explanation: Fusion of hydrogen to helium produces photons, light, and heat.
61. Proton-proton chain is dominant in:
a) Sun-like stars
b) Massive stars
c) White dwarfs
d) Neutron stars
Answer: a
Explanation: Fusion of H → He in low-mass stars mainly via proton-proton chain.
62. CNO cycle is dominant in:
a) Massive stars (>1.3 solar masses)
b) Sun
c) White dwarfs
d) All stars equally
Answer: a
Explanation: Carbon acts as catalyst in hydrogen fusion in massive stars.
63. Helium burning in stars produces:
a) Carbon and oxygen
b) Hydrogen
c) Nitrogen
d) Neon
Answer: a
Explanation: Fusion of 3 He nuclei → C-12, also produces O-16 via α-capture.
64. Fusion reactions in stars are exothermic because:
a) Binding energy per nucleon increases
b) Decreases
c) Remains same
d) None
Answer: a
Explanation: Products are more tightly bound → energy released.
65. Energy transport in stars occurs via:
a) Radiation, convection, conduction
b) Only radiation
c) Only conduction
d) Only convection
Answer: a
Explanation: Core energy moves outward by radiation or convection depending on opacity.
66. Fusion reactions produce:
a) Neutrinos
b) Photons
c) Kinetic energy of particles
d) All of the above
Answer: d
Explanation: Energy appears in multiple forms, detectable by solar neutrinos.
67. Sun’s core temperature:
a) ~1.5 × 10⁷ K
b) 10⁴ K
c) 10⁵ K
d) 10⁶ K
Answer: a
Explanation: High enough for proton-proton fusion chain.
68. Lawson criterion defines:
a) Condition for energy gain in fusion
b) Condition for fission
c) Neutron lifetime
d) Alpha decay rate
Answer: a
Explanation: Product of plasma density, confinement time, and temperature must exceed critical value.
69. Tokamak uses:
a) Magnetic confinement
b) Laser confinement
c) Chemical confinement
d) None
Answer: a
Explanation: Toroidal magnetic field confines hot plasma for fusion experiments.
70. Inertial confinement fusion uses:
a) Lasers or ion beams to compress fuel pellet
b) Magnetic field
c) Gas cooling
d) Chemical explosives
Answer: a
Explanation: Rapid compression heats plasma to fusion temperatures briefly.
71. Deuterium in fusion reactors is obtained from:
a) Sea water
b) Uranium ore
c) Graphite
d) Lead
Answer: a
Explanation: D/H ratio in water is sufficient for fusion fuel.
72. Tritium in reactors is produced by:
a) Lithium + neutron → Tritium + Helium
b) Deuterium only
c) Uranium decay
d) Fission of Pu
Answer: a
Explanation: Tritium is rare naturally; produced in situ via Li-6 reactions.
73. Energy released per gram of fusion fuel is:
a) ~10⁷ times chemical energy
b) Same as chemical
c) Less
d) Zero
Answer: a
Explanation: Extremely high energy density per mass of hydrogen isotopes.
74. Fusion in stars maintains:
a) Hydrostatic equilibrium
b) Nuclear fission
c) Chemical balance
d) Magnetic equilibrium
Answer: a
Explanation: Outward radiation pressure balances gravitational pull.
75. Fusion reactions are considered:
a) Clean energy source
b) Polluting
c) Radioactive only
d) Chemical
Answer: a
Explanation: Minimal radioactive waste, no greenhouse gases.
76. Fusion reactors aim to use which reaction first commercially?
a) Deuterium–Tritium (D-T) fusion
b) Deuterium–Deuterium (D-D) fusion
c) Proton–Proton fusion
d) Carbon–Nitrogen fusion
Answer: a
Explanation: D-T reaction has highest cross-section at achievable temperatures (~100 million K).
77. Energy released in D-T fusion per reaction:
a) 17.6 MeV
b) 200 MeV
c) 1 MeV
d) 100 MeV
Answer: a
Explanation: 3.5 MeV carried by alpha, 14.1 MeV by neutron.
78. Fusion fuel advantage over fission:
a) Abundant, less radioactive waste
b) Scarce fuel
c) More long-lived waste
d) Difficult to obtain
Answer: a
Explanation: Deuterium abundant in sea water; Tritium can be bred; minimal long-lived waste.
79. Fission vs. Fusion: Energy per kg:
a) Fusion > Fission > Chemical
b) Fission > Fusion
c) Chemical > Fusion
d) Fission = Fusion
Answer: a
Explanation: Fusion releases ~10⁷ times chemical energy; Fission ~10⁶ times.
80. Stellar nucleosynthesis produces elements:
a) H → He → C → O → Fe
b) Only H → He
c) Only Fe
d) None
Answer: a
Explanation: Fusion in stars forms heavier elements until iron, beyond which fusion is endothermic.
81. Hydrogen bombs use:
a) Fission + Fusion (Teller-Ulam design)
b) Fission only
c) Fusion only
d) Chemical explosive
Answer: a
Explanation: Fission primary compresses fusion fuel to trigger D-T fusion.
82. Magnetic confinement fusion device:
a) Tokamak
b) Nuclear reactor
c) Bubble chamber
d) Cloud chamber
Answer: a
Explanation: Magnetic fields confine plasma at millions of K.
83. Inertial confinement fusion uses:
a) High-power lasers
b) Magnetic fields
c) Chemical reactions
d) Nuclear fission
Answer: a
Explanation: Laser energy compresses fuel pellet to achieve necessary temperature & pressure.
84. Tritium breeding reaction in fusion:
a) Li-6 + n → T + He-4
b) H-2 + n → T
c) He-3 + n → T
d) U-238 + n → T
Answer: a
Explanation: Essential to sustain D-T fuel cycle in reactors.
85. Fusion reactors face main challenge:
a) Achieving confinement, temperature, and density simultaneously
b) Fuel scarcity
c) Waste disposal
d) Low energy output
Answer: a
Explanation: Plasma confinement at extreme conditions is technologically difficult.
86. Energy gain factor (Q) in fusion:
a) Ratio of fusion power output to power input
b) Efficiency of fission
c) Efficiency of chemical reaction
d) None
Answer: a
Explanation: Q > 1 needed for net energy gain.
87. ITER project aims at:
a) Demonstrating net energy gain from D-T fusion
b) Fission reactor efficiency
c) Solar power
d) Chemical battery
Answer: a
Explanation: International Thermonuclear Experimental Reactor; Tokamak design.
88. Advantages of fusion over fission:
a) More energy per kg, abundant fuel, safer, less long-lived waste
b) Less energy
c) Less safe
d) Rare fuel
Answer: a
Explanation: Fusion has higher energy density and minimal long-lived radioactive products.
89. Disadvantage of fission over fusion:
a) Radioactive waste
b) Requires high temperature
c) Fuel abundant
d) Minimal radiation
Answer: a
Explanation: Fission produces long-lived fission products.
90. Helium-3 fusion is considered:
a) Aneutronic, cleaner reaction
b) Produces many neutrons
c) Produces long-lived waste
d) Not energy efficient
Answer: a
Explanation: ³He + D → ⁴He + proton; minimal neutron emission → cleaner.
91. Fusion reactor plasma is typically:
a) Fully ionized gas (plasma)
b) Solid
c) Liquid
d) Gas only
Answer: a
Explanation: High temperature ionizes fuel, forming plasma for fusion reactions.
92. Lawson criterion states:
a) n τ T ≥ critical value for net energy gain
b) Critical mass for fission
c) Energy released in fission
d) Temperature of sun
Answer: a
Explanation: Product of density (n), confinement time (τ), and temperature (T) must exceed threshold.
93. Fusion in stars vs. reactors:
a) Stars: gravitational confinement, reactors: magnetic/inertial
b) Both chemical
c) Stars fission only
d) Both magnetic
Answer: a
Explanation: Gravity in stars substitutes for confinement; reactors need artificial confinement.
94. Energy released in one gram of D-T fuel:
a) ~340 GJ
b) 1 MJ
c) 1 GJ
d) 1 kJ
Answer: a
Explanation: Extremely high energy density compared to chemical fuels.
95. Fission vs Fusion: Waste type
a) Fusion → short-lived, fission → long-lived
b) Both same
c) Fusion → long-lived
d) Fission → short-lived
Answer: a
Explanation: Fusion products mostly short-lived; fission products like Cs-137 last decades.
96. Tritium handling in fusion:
a) Requires containment due to radioactivity
b) Stable, no containment
c) Solid fuel only
d) Non-radioactive
Answer: a
Explanation: Beta emitter; precautions needed for environmental safety.
97. Fusion energy advantage for space:
a) High energy density, less mass
b) Low energy
c) Produces chemical waste
d) Requires fission
Answer: a
Explanation: Efficient, minimal fuel mass for spacecraft propulsion.
98. Stellar evolution ends when:
a) Core iron forms, fusion stops
b) Hydrogen exhausted only
c) Carbon burns completely
d) Stars explode randomly
Answer: a
Explanation: Iron fusion is endothermic → star collapses → supernova or white dwarf.
99. Neutron flux in fission reactor:
a) Determines reaction rate
b) Determines fuel mass only
c) Determines temperature only
d) Not important
Answer: a
Explanation: Higher flux → more fission events per second.
100. Comparison summary:
a) Fusion: cleaner, more energy, abundant fuel; Fission: radioactive waste, limited fuel
b) Fusion: less energy; Fission: more energy
c) Both same
d) None
Answer: a
Explanation: Fusion is ultimate goal for clean energy; fission currently commercial but has waste issues.