WAEC Physics 2021 Theory — Question 27
Question 27 of 35 from the West African Examinations Council (WAEC) Physics 2021 Theory paper, with the correct answer and a full explanation.
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12(a). (i) State the principal factor that determines the relative stability of a radioactive nucleus. (ii) Arrange the radionuclides ⁴⁰₂₀X, ⁹²₃₆W and ⁹²₄₂Y in decreasing order of stability. Justify your answer.
Model answer
(i) The neutron-to-proton (n:p) ratio of the nucleus is the principal factor determining its relative stability. (ii) n:p ratios: X = 20/20 = 1.0; Y = 53/42 ≈ 1.26; W = 56/36 ≈ 1.56. The ratio closest to 1 is most stable, so decreasing order of stability: X > Y > W.
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