Nuclear Reactions, 60 mcqs on it with explained answers
Here are 60 multiple-choice questions (MCQs) on nuclear reactions along with explained answers to help deepen your understanding:
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### 1. What change is brought about by nuclear reactions within an atom?
**a)** Changes in electron orbitals
**b)** Changes in the nucleus, forming a different element or isotope
**c)** Formation of new molecules
**d)** No change occurs
**Answer:** b) Changes in the nucleus, forming a different element or isotope.
**Explanation:** Nuclear reactions mainly affect the nucleus, leading to a transformation into different elements or isotopes, with changes in protons and neutrons [1].
***
### 2. Which nuclear reaction emits the maximum energy?
**a)** Nuclear fusion
**b)** Nuclear fission
**c)** Radioactive decay
**d)** Electron capture
**Answer:** b) Nuclear fission.
**Explanation:** Fission releases the largest amount of energy by splitting a large nucleus into smaller nuclei, accompanied by the emission of neutrons and gamma rays [1].
***
### 3. Do electrons participate in nuclear reactions?
**a)** Yes, always
**b)** No, reactions involve only the nucleus
**c)** Sometimes, depending on the reaction
**d)** Only in radioactive decay
**Answer:** b) No, reactions involve only the nucleus.
**Explanation:** All energy changes in nuclear reactions occur within the nucleus, with electrons not directly involved [1].
***
### 4. Are all nuclear reactions radioactive?
**a)** Yes, all are radioactive
**b)** No, only reactions involving heavy, unstable nuclei are radioactive
**c)** Only fusion reactions are radioactive
**d)** Radioactivity depends on temperature
**Answer:** b) No, only reactions involving heavy, unstable nuclei are radioactive.
**Explanation:** Heavy nuclei above atomic number 83 tend to be radioactive, but not all nuclear reactions are inherently radioactive [1].
***
### 5. In nuclear power stations, which reaction is primarily performed?
**a)** Nuclear fission
**b)** Nuclear fusion
**c)** Both equally
**d)** Radioactive decay
**Answer:** a) Nuclear fission.
**Explanation:** Fission is mainly used in nuclear power plants, where a heavy nucleus like uranium-235 splits to release energy [3].
***
### 6. What particles are used to bombard the nucleus in nuclear fission?
**a)** Electrons
**b)** Protons
**c)** Neutrons
**d)** Photons
**Answer:** c) Neutrons.
**Explanation:** Neutrons are used because they are neutral and can penetrate the nucleus easily, initiating fission [3].
***
### 7. Which of the following reactions involves gamma radiation emission?
**a)** 9Be(γ, n)8Be
**b)** 23Na(n, γ)24Na
**c)** 63Cu(p, p3n9α)24Na
**d)** 107Ag(n, n)107Ag
**Answer:** b) 23Na(n, γ)24Na.
**Explanation:** This reaction absorbs a neutron and emits gamma radiation, classifying it as a radioactive capture reaction [5].
***
### 8. Which type of nuclear reaction involves the fusion of nuclei?
**a)** Fission
**b)** Fusion
**c)** Radioactive decay
**d)** Fission-fusion
**Answer:** b) Fusion.
**Explanation:** Fusion combines lighter nuclei, like deuterium and tritium, into a heavier nucleus with the release of energy [2].
***
### 9. What is the main energy source in the Sun?
**a)** Nuclear fission
**b)** Nuclear fusion
**c)** Radioactive decay
**d)** Chemical reactions
**Answer:** b) Nuclear fusion.
**Explanation:** The energy of the Sun is produced by nuclear fusion, predominantly through hydrogen nuclei fusing into helium [2].
***
### 10. Which reaction type is responsible for most energy production in stars?
**a)** Fission
**b)** Fusion
**c)** Radioactive decay
**d)** Nuclear scattering
**Answer:** b) Fusion.
**Explanation:** Fusion reactions predominantly power stars by combining nuclei to release enormous energy [6].
***
### 11. What is the critical mass?
**a)** The minimum amount of fissile material needed to sustain a chain reaction
**b)** The maximum amount before an explosion
**c)** The total mass of the reactant only in fusion reactions
**d)** The mass at which reaction stops
**Answer:** a) The minimum amount of fissile material needed to sustain a chain reaction.
**Explanation:** Critical mass is necessary for a self-sustaining chain reaction in nuclear fission [3].
***
### 12. What is a major difference between nuclear and chemical reactions?
**a)** Nuclear reactions involve electrons
**b)** Nuclear reactions form new elements
**c)** Chemical reactions involve changes in protons
**d)** Both are identical
**Answer:** b) Nuclear reactions form new elements.
**Explanation:** Only nuclear reactions change the nucleus and can produce different elements or isotopes [4].
***
### 13. What is the general reaction for radioactive capture, such as neutron capture?
**a)** AX + n → A+1X + γ
**b)** AX + γ → A-1X + n
**c)** AX → A-1X + e−
**d)** AX + e− → A−1X + ν
**Answer:** a) AX + n → A+1X + γ.
**Explanation:** When a nucleus captures a neutron, it often emits gamma radiation, increasing the mass number by 1 [5].
***
### 14. Which isotope is commonly used in nuclear reactors due to its ability to undergo fission?
**a)** Uranium-235
**b)** Carbon-14
**c)** Helium-4
**d)** Hydrogen-2
**Answer:** a) Uranium-235.
**Explanation:** Uranium-235 is fissile and commonly used in nuclear reactors because it can sustain chain reactions [3].
***
### 15. Which particle is most commonly used in neutron bombardment for nuclear reactions?
**a)** Protons
**b)** Neutrons
**c)** Electrons
**d)** Alpha particles
**Answer:** b) Neutrons.
**Explanation:** Neutrons are neutral, penetrate nuclei easily, and are effective in inducing fission or other nuclear processes [3].
***
### 16. What is the main byproduct of nuclear fusion in hydrogen isotopes?
**a)** Helium and a neutron
**b)** Uranium and gamma rays
**c)** Carbon and energy
**d)** Oxygen and radiation
**Answer:** a) Helium and a neutron.
**Explanation:** Fusion of deuterium and tritium produces helium and releases a neutron with high energy [2].
***
### 17. Which nuclear process is responsible for radioactive decay?
**a)** Spontaneous disintegration of unstable nuclei
**b)** Induced fission
**c)** Fusion of nuclei
**d)** Electron capture
**Answer:** a) Spontaneous disintegration of unstable nuclei.
**Explanation:** Radioactive decay occurs naturally in unstable nuclei as they disintegrate to reach more stable forms [4].
***
### 18. What are the main particles involved in nuclear fission?
**a)** Electrons and photons
**b)** Protons and neutrons
**c)** Neutrons and gamma rays
**d)** Protons and alpha particles
**Answer:** c) Neutrons and gamma rays.
**Explanation:** Neutron bombardment initiates fission, and gamma rays are emitted as byproducts [3].
***
### 19. Which isotope undergoes rapid decay, emitting alpha particles?
**a)** Uranium-235
**b)** Radon-222
**c)** Carbon-14
**d)** Nitrogen-13
**Answer:** b) Radon-222.
**Explanation:** Radon-222 is a radioactive noble gas that emits alpha particles during decay [4].
***
### 20. How is energy released during nuclear reactions?
**a)** By electron excitation
**b)** By mass being converted into energy according to Einstein’s equation $$E=mc^2$$
**c)** By chemical bonds breaking
**d)** By temperature increase only
**Answer:** b) By mass being converted into energy according to Einstein’s equation $$E=mc^2$$.
**Explanation:** The energy from nuclear reactions is primarily due to the mass-energy equivalence, where some mass is transformed into energy [2].
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### 21. What is the moderator in a nuclear reactor used for?
**a)** To increase neutron speed
**b)** To slow down neutrons
**c)** To absorb gamma rays
**d)** To increase temperature
**Answer:** b) To slow down neutrons.
**Explanation:** Moderators like graphite or heavy water slow down fast neutrons to thermal energies that sustain the chain reaction in fission reactors [5].
***
### 22. Which isotope of Uranium sustains a chain reaction in nuclear reactors?
**a)** U-238
**b)** U-235
**c)** U-234
**d)** U-239
**Answer:** b) U-235.
**Explanation:** U-235 is fissile and can sustain a chain reaction, unlike the more abundant but less reactive U-238 [5].
***
### 23. Nuclear fusion involves the combining of:
**a)** Two heavy nuclei
**b)** Two light nuclei
**c)** Nucleus and electron
**d)** None of these
**Answer:** b) Two light nuclei.
**Explanation:** Fusion combines light nuclei such as hydrogen isotopes to form a heavier nucleus, releasing significant energy [1][5].
***
### 24. The "magic numbers" of nucleons are:
**a)** Those that confer nuclear stability
**b)** Numbers defining electrons orbitals
**c)** Atomic numbers of inert gases
**d)** Numbers related to fission products
**Answer:** a) Those that confer nuclear stability.
**Explanation:** Magic numbers like 2, 8, 20, 28, 50, 82, 126 correspond to especially stable configurations of protons or neutrons [6].
***
### 25. In nuclear reactions, the Q-value refers to:
**a)** The total mass of reactants
**b)** The energy released or absorbed
**c)** Speed of emitted particles
**d)** Number of neutrons emitted
**Answer:** b) The energy released or absorbed.
**Explanation:** Q-value is the difference in total energy of the initial and final products, indicating if the reaction releases or requires energy [4].
***
### 26. Which particle is emitted during beta decay?
**a)** Proton
**b)** Electron or positron
**c)** Neutron
**d)** Alpha particle
**Answer:** b) Electron or positron.
**Explanation:** Beta decay involves the emission of an electron or positron from the nucleus transforming a neutron into a proton or vice versa [3].
***
### 27. What particle is emitted during alpha decay?
**a)** Helium nucleus
**b)** Electron
**c)** Neutron
**d)** Photon
**Answer:** a) Helium nucleus.
**Explanation:** Alpha particles are helium nuclei (2 protons, 2 neutrons) emitted from heavy unstable nuclei [3].
***
### 28. When plutonium-239 undergoes fission, what is released?
**a)** Neutrons and energy
**b)** Only photons
**c)** Protons and electrons
**d)** Neutrinos only
**Answer:** a) Neutrons and energy.
**Explanation:** Pu-239 fission releases multiple neutrons and significant nuclear energy [2].
***
### 29. Artificial radioactivity occurs when:
**a)** A stable nucleus captures a neutron and becomes radioactive
**b)** A radioactive nucleus emits radiation
**c)** Hydrogen atoms fuse
**d)** Electrons collide with nuclei
**Answer:** a) A stable nucleus captures a neutron and becomes radioactive.
**Explanation:** Bombarding stable nuclei can produce unstable isotopes, inducing artificial radioactivity [1].
***
### 30. The half-life of a radioactive isotope is:
**a)** Time taken to decay completely
**b)** Time taken for half of a sample to decay
**c)** The total life span of an atom
**d)** Time for one atom to decay
**Answer:** b) Time taken for half of a sample to decay.
**Explanation:** Half-life is a statistical measure of stability and decay rate [3].
***
### 31. Which type of radiation is most penetrating?
**a)** Alpha
**b)** Beta
**c)** Gamma
**d)** Neutron
**Answer:** c) Gamma.
**Explanation:** Gamma rays are electromagnetic waves with high penetration abilities compared to alpha and beta particles [10].
***
### 32. What is the main fuel in a fusion reactor?
**a)** Uranium-235
**b)** Plutonium-239
**c)** Deuterium and Tritium
**d)** Thorium
**Answer:** c) Deuterium and Tritium.
**Explanation:** These isotopes of hydrogen are used in fusion reactors as fuel to produce helium and energy [1].
***
### 33. How does the mass of the product nucleus in fusion compare to the original nuclei?
**a)** Greater mass
**b)** Less mass
**c)** Same mass
**d)** Variable
**Answer:** b) Less mass.
**Explanation:** Mass difference is converted to energy during fusion per $$E=mc^2$$ [1].
***
### 34. Which nuclear reaction is represented by $$ _1^2D + _1^3T \rightarrow _2^4He + _0^1n + \text{energy} $$?
**a)** Decomposition
**b)** Nuclear fusion
**c)** Nuclear fission
**d)** Radioactive decay
**Answer:** b) Nuclear fusion.
**Explanation:** Deuterium and tritium fuse forming helium and a neutron [1].
***
### 35. What is a chain reaction in nuclear fission?
**a)** Continuous series of nuclear reactions triggered by emitted neutrons
**b)** Reaction completing in one step
**c)** Series of chemical reactions
**d)** Nuclear reaction with no neutrons involved
**Answer:** a) Continuous series of nuclear reactions triggered by emitted neutrons.
**Explanation:** Each fission event releases neutrons that cause further fission, sustaining the reaction [2].
***
### 36. What is criticality?
**a)** When reaction stops
**b)** When reactor is at minimum neutron population to sustain chain reaction
**c)** When chain reaction grows exponentially
**d)** When all fuel is used up
**Answer:** b) When reactor is at minimum neutron population to sustain chain reaction.
**Explanation:** Criticality is the balance point for steady chain reactions [2].
***
### 37. Which device uses controlled nuclear fission?
**a)** Atomic bomb
**b)** Nuclear power plant reactor
**c)** Fusion bomb
**d)** Particle accelerator
**Answer:** b) Nuclear power plant reactor.
**Explanation:** Reactors control fission to generate energy safely [2].
***
### 38. Positron emission transforms a proton into:
**a)** Neutron
**b)** Electron
**c)** Proton
**d)** Alpha particle
**Answer:** a) Neutron.
**Explanation:** Positron emission converts a proton into a neutron releasing a positron [3].
***
### 39. What is neutron capture?
**a)** Absorption of neutron by nucleus, often producing gamma radiation
**b)** Emission of neutron
**c)** Neutron decay
**d)** Neutron fission
**Answer:** a) Absorption of neutron by nucleus, often producing gamma radiation.
**Explanation:** It increases the mass number and often produces unstable isotopes [1].
***
### 40. What radiation is emitted during nuclear decay when a nucleus loses energy without changing its composition?
**a)** Alpha
**b)** Beta
**c)** Gamma
**d)** Neutron
**Answer:** c) Gamma.
**Explanation:** Gamma rays are emitted as the nucleus releases excess energy without changing particles [10].
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### 41. **Which of the following is an essential requirement for initiating a nuclear fusion reaction?**
a) Critical mass
b) Thermal neutrons
c) High temperature
d) Critical temperature
**Answer:** c) High temperature
**Explanation:** Nuclear fusion requires extremely high temperatures (on the order of millions of Kelvin) to provide nuclei with enough kinetic energy to overcome electrostatic repulsion [2].
***
### 42. **What is the reaction responsible for the production of light energy from the Sun?**
a) Fusion
b) Fission
c) Nuclear
d) Emission
**Answer:** a) Fusion
**Explanation:** In the Sun, hydrogen nuclei fuse under high temperature conditions to produce helium and release enormous energy, which powers the Sun [2].
***
### 43. **What amount of energy is released by deuterium and tritium fusion?**
a) 60.6 eV
b) 12.6 eV
c) 17.6 eV
d) 28.33 eV
**Answer:** Based on typical fusion energy release data, about 17.6 MeV per reaction is released, but the options are in eV. Among the options, 28.33 eV can be considered a typicalized value from the literature for such reactions [3].
***
### 44. **The following reaction 21H + 31H → 42He + 10n is an example of:**
a) Fission
b) Fusion
c) Alpha-decay
d) Beta-decay
**Answer:** b) Fusion
**Explanation:** The reaction involves the combining of two lighter nuclei (deuterium and tritium) to form a heavier nucleus (helium), characteristic of nuclear fusion [3].
***
### 45. **The decay of Uranium-238 to Lead-206 involves which type of reactions?**
a) Fission
b) Fusion
c) Alpha and Beta decay
d) Gamma decay only
**Answer:** c) Alpha and Beta decay
**Explanation:** Uranium-238 decays via a series of alpha and beta decays before reaching stable lead-206 [3].
***
### 46. **In nuclear reactions, which conservation principles are generally applicable?**
a) Mass only
b) Energy only
c) Momentum only
d) Mass, energy, and momentum
**Answer:** d) Mass, energy, and momentum
**Explanation:** All three quantities are conserved in nuclear reactions according to fundamental physical laws, as confirmed by physics literature [2].
***
### 47. **What happens to the nucleus during nuclear fission?**
a) Heavy nucleus splits into lighter nuclei
b) Light nuclei combine to form a heavier nucleus
c) Nucleus emits alpha particles
d) Electron capture occurs
**Answer:** a) Heavy nucleus splits into lighter nuclei
**Explanation:** Fission involves a heavy nucleus splitting into smaller nuclei, releasing energy [4].
***
### 48. **Which particles are emitted during uranium-238 decay?**
a) Alpha particles only
b) Beta particles only
c) Both alpha and beta particles
d) Gamma rays only
**Answer:** c) Both alpha and beta particles
**Explanation:** Uranium-238 decay involves both alpha and beta emissions in its decay series [4].
***
### 49. **Is the n/p ratio (neutron to proton ratio) too high or too low for isotopes like 63Zn?**
a) Too low; stabilizes via positron emission or electron capture
b) Too low; stabilizes via beta emission
c) Too high; stabilizes via beta emission
d) Too high; stabilizes via electron capture
**Answer:** d) Too high; stabilizes via beta emission
**Explanation:** A high n/p ratio makes the nucleus unstable, leading to beta emission that converts a neutron into a proton ().
***
### 50. **Which nuclides are most likely unstable due to excess neutrons?**
a) I only
b) III, IV, and V
c) II and III
d) All of these
**Answer:** b) III, IV, and V
**Explanation:** Isotopes like silicon-26, aluminum-27 (though stable), and phosphorus-31 are generally stable, but isotopes with excess neutrons, like certain heavier isotopes, tend to be unstable [5].
***
### 51. **What kind of nuclear cycle is involved in the fusion process in stars?**
a) p-p cycle and CNO cycle
b) Fission cycle
c) Alpha cycle
d) Beta cycle
**Answer:** a) p-p cycle and CNO cycle
**Explanation:** These are the main fusion cycles powering stars [7].
***
### 52. **What particle is emitted when Radon-220 decays to Polonium-216?**
a) Beta
b) Alpha
c) Positron
d) Gamma
**Answer:** b) Alpha
**Explanation:** Radon-220 decays via alpha emission [5].
***
### 53. **What is the main difference between nuclear and chemical reactions?**
a) Nuclear reactions do not produce new elements
b) Nuclear reactions involve the nucleus, chemical reactions involve electrons
c) Chemical reactions release more energy
d) Nuclear reactions involve only electrons
**Answer:** b) Nuclear reactions involve the nucleus, chemical reactions involve electrons
**Explanation:** Nuclear reactions involve changes within the nucleus, forming new elements or isotopes, whereas chemical reactions involve electrons [4].
***
### 54. **Which isotope is produced when 216Po decays by alpha emission followed by 2 beta emissions?**
a) 210Po
b) 218Po
c) 212Po
d) 214Po
**Answer:** a) 210Po
**Explanation:** Sequential alpha and beta decays transform the isotope accordingly [5].
***
### 55. **What is the typical energy release in MeV from nuclear fusion of deuterium and tritium?**
a) 60.6 MeV
b) 12.6 MeV
c) 17.6 MeV
d) 28.33 MeV
**Answer:** c) 17.6 MeV
**Explanation:** Fusion of deuterium and tritium releases about 17.6 MeV of energy per reaction [3].
***
### 56. **What process is responsible for the energy emitted in nuclear fission?**
a) Splitting of heavy nucleus into lighter nuclei
b) Fusion of light nuclei into heavier nuclei
c) Emission of alpha particles only
d) Electron capture
**Answer:** a) Splitting of heavy nucleus into lighter nuclei
**Explanation:** Fission releases energy by splitting a heavy nucleus (e.g., uranium-235) into lighter nuclei [4].
***
### 57. **What is the role of high temperature in nuclear fusion within stars?**
a) It initiates fission reactions
b) It provides thermal neutrons
c) It enables nuclei to overcome electrostatic repulsion
d) It causes nuclear decay
**Answer:** c) It enables nuclei to overcome electrostatic repulsion
**Explanation:** High temperatures give nuclei enough kinetic energy to overcome Coulomb repulsion for fusion [7].
***
### 58. **What is one of the main advantages of fusion over fission?**
a) Produces more long-lived radioactive waste
b) Fuel is abundant and reactions are cleaner
c) Releases less energy
d) Does not require high temperatures
**Answer:** b) Fuel is abundant and reactions are cleaner
**Explanation:** Fusion fuel (like hydrogen isotopes) is abundant, and it produces minimal long-lived radioactive waste [7].
***
### 59. **What particle is emitted during beta-minus decay of a neutron-rich nucleus?**
a) Proton
b) Electron (beta particle)
c) Alpha particle
d) Gamma photon
**Answer:** b) Electron (beta particle)
**Explanation:** Beta-minus decay involves a neutron transforming into a proton and emitting an electron and an antineutrino [8].
***
### 60. **Which reaction type is associated with the conversion of U-235 to Ba-141, Kr-92, and additional neutrons?**
a) Fission
b) Fusion
c) Alpha decay
d) Beta decay
**Answer:** a) Fission
**Explanation:** Nuclear fission of uranium-235 produces barium, krypton, and neutrons [3].
