Half-life of iodine-131 is 8 days. If 20mg is present initially. How much iodine is left behind after 2 half-lives?
Correct answer: B. 5 mg
- A. 10 mg
- B. 5 mg
- C. 2.5 mg
- D. 1.25 mg
Explanation
After a single half-life, the substance becomes half of its original mass. For iodine, after 1 half-life, the mass of iodine becomes 20/2=10mg. Then after the second half-life, this 10mg is further reduced by half to give 5mg.
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