Nuclear Chemistry Quiz

Grade 11 · Science · Quiz

10 questions on radioactive decay types, half-life calculations, fission vs. fusion, and nuclear equations.

Questions

1. Which type of radiation has the lowest penetrating power?

   1. Alpha
   2. Beta
   3. Gamma
   4. X-ray
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   Answer: Alpha

   Alpha particles (⁴He nuclei) are large, doubly charged, and stopped by a sheet of paper or a few centimeters of air.

2. In beta-minus decay, what particle is emitted?

   1. Proton
   2. Neutron
   3. Electron
   4. Positron
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   Answer: Electron

   In β⁻ decay, a neutron converts to a proton and emits a high-energy electron (and antineutrino). Atomic number increases by 1.

3. Carbon-14 has a half-life of 5,730 years. A sample has 100 g. How much remains after 11,460 years?

   1. 50 g
   2. 25 g
   3. 12.5 g
   4. 6.25 g
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   Answer: 25 g

   11,460 years = 2 half-lives. Remaining = 100 × (1/2)² = 100 × 1/4 = 25 g.

4. In a nuclear equation, what two quantities are conserved?

   1. Proton count and neutron count only
   2. Mass number and atomic number
   3. Energy and velocity
   4. Electron count and charge
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   Answer: Mass number and atomic number

   Nuclear equations must balance with equal mass numbers (A) and atomic numbers (Z) on both sides.

5. Uranium-235 undergoes fission when struck by a neutron. This can trigger more fissions because:

   1. It releases gamma rays that ionize nearby atoms
   2. It releases additional neutrons that can split more U-235 nuclei
   3. It raises the temperature causing thermal runaway
   4. It produces alpha particles that are highly reactive
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   Answer: It releases additional neutrons that can split more U-235 nuclei

   Fission of U-235 releases 2–3 neutrons per event. These can trigger further fissions, creating a self-sustaining chain reaction.

6. What is the source of energy in nuclear reactions according to Einstein's equation?

   1. Chemical bond breaking
   2. Electron energy transitions
   3. Conversion of mass to energy (E = mc²)
   4. Thermal expansion of the nucleus
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   Answer: Conversion of mass to energy (E = mc²)

   The mass defect (difference between reactant and product masses) is converted to energy. Even tiny mass changes yield enormous energy because c² is huge.

7. Which isotope is commonly used for radiocarbon dating of organic material?

   1. C-12
   2. C-13
   3. C-14
   4. U-238
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   Answer: C-14

   C-14 has a half-life of ~5,730 years and is incorporated into living organisms. After death, C-14 decays and the remaining fraction indicates age.

8. Gamma decay changes which properties of the nucleus?

   1. Atomic number only
   2. Mass number only
   3. Both atomic number and mass number
   4. Neither atomic number nor mass number
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   Answer: Neither atomic number nor mass number

   Gamma decay releases energy as a photon from an excited nucleus. No particles are emitted, so Z and A remain unchanged.

9. Nuclear fusion requires extremely high temperatures primarily because:

   1. High temperature increases nuclear size
   2. Nuclei must overcome electrostatic repulsion to get close enough to fuse
   3. Low temperature prevents gamma radiation
   4. Neutrons must be slowed down
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   Answer: Nuclei must overcome electrostatic repulsion to get close enough to fuse

   Like-charged protons repel each other. Only at temperatures of tens of millions of Kelvin do nuclei have enough kinetic energy to overcome this Coulomb barrier.

10. Complete the nuclear equation: ²³⁸₉₂U → ⁴₂He + ___

    1. ²³⁴₉₀Th
    2. ²³⁴₉₁Pa
    3. ²³⁶₉₀Th
    4. ²³²₈₈Ra
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    Answer: ²³⁴₉₀Th

    Alpha decay: mass number 238 − 4 = 234; atomic number 92 − 2 = 90. Product is thorium-234 (²³⁴₉₀Th).

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