Chemistry Clarity · chemistryclarity.com

Nuclear Stability: Quiz

Seven questions on the band of stability, N/Z ratios, predicting decay modes and decay series, with explanations.

7 questionsIntermediate

7 questions

  1. Question 1EasyWhat force holds protons and neutrons together in the nucleus?
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    Answer: The strong nuclear force

    The strong force attracts all nucleons over very short distances, overcoming the repulsion between protons.

  2. Question 2EasyIodine-131 has more neutrons than the stable iodine-127. How does it decay?
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    Answer: Beta-minus decay

    Too many neutrons: a neutron changes into a proton (β⁻), lowering N/Z towards the band of stability.

  3. Question 3MediumFluorine-18 has fewer neutrons than the stable fluorine-19. How does it decay?
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    Answer: Positron emission

    Too many protons for its neutrons: a proton becomes a neutron by emitting a positron. This is why F-18 is used in PET scans.

  4. Question 4MediumWhich nucleus is most likely to undergo alpha decay?
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    Answer: Polonium-210

    Polonium (Z = 84) is beyond Z = 83, so it is too large and decays by alpha emission. C-14 and Co-60 are β⁻ emitters; Na-22 is a β⁺ emitter.

  5. Question 5MediumWhat is the N/Z ratio of lead-206 (Z = 82)?
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    Answer: 1.51

    N = 206 − 82 = 124; N/Z = 124 ÷ 82 = 1.51. Heavy stable nuclei need about 1.5 neutrons per proton.

  6. Question 6HardThorium-232 decays through a series to lead-208. How many alpha decays occur?
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    Answer: 6

    Only alpha decay changes the mass number: (232 − 208) ÷ 4 = 6 alpha decays.

  7. Question 7HardIn the series Th-232 → Pb-208 (Z: 90 → 82), how many beta-minus decays occur?
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    Answer: 4

    6 alpha decays lower Z by 12, to 78. Lead has Z = 82, so Z must rise by 4: 4 β⁻ decays.