A certain substance has a half-life of 5.0 hours. How many nuclei of the substance are required to give an initial activity of 6.0 μCi? 1 Ci = 3.7 × 10¹⁰Bq. A) 5.8 × 10⁹ B) 8.5 × 10⁸ C) 6.3 × 10⁸ D) 3.2 × 10⁹ E) 2.4 × 10⁹

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The activity (A) is related to the number of nuclei (N) by A = λN, where λ is the decay constant. λ = ln(2) / half-life. Convert 6.0 μCi to Bq: 6.0 μCi = 6.0 × 10^-6 × 3.7 × 10^10 Bq. Calculate λ using the half-life of 5.0 hours (convert to seconds). Solve for N using N = A / λ.

A Certain Substance Has a Half-Life of 5