Engineering Board Exam Reviewer · Chemistry · medium

A 100 mg sample of iodine-131 (half-life 8 days) is stored for 24 days. How much remains?

1. 12.5 mg
2. 25.0 mg
3. 33.3 mg
4. 0.0 mg

Answer

A. 12.5 mg

Solution

24 days = 3 half-lives: 100(1/2)3 = 12.5 mg.

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