The half-life of iodine-131 is 8 days and its weight is 20 mg. After 4 half-lives, the amount left undecayed will be:
Correct answer: C. 1.25 mg
- A. 2.5 mg
- B. 0.625 mg
- C. 1.25 mg
- D. 0.3125 mg
Explanation
The amount remaining after n half. lives is the initial amount divided by 2ⁿ. In this case, n=4, so the remaining amount is 20 mg / 2⁴ = 20 mg / 16 = 1.25 mg.
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