Radioactive kcSr has a half-life of 30 years. What percent of a sample of kcSr will remain after 90 years?
Correct answer: B. 12.5%
- A. 0%
- B. 12.5%
- C. 50%
- D. 75%
Explanation
To solve the question, we first determine how many half-lives have passed in 90 years. Given the half-life of kcSr is 30 years, we calculate:90 years ÷ 30 years/half-life = 3 half-lives.After each half-life, the remaining percentage of the original sample is halved. Starting with 100%:After 1 half-life (30 years): 100% ÷ 2 = 50%After 2 half-lives (60 years): 50% ÷ 2 = 25%After 3 half-lives (90 years): 25% ÷ 2 = 12.5%Thus, 12.5% of the original kcSr sample remains after 90 years. The other options are incorrect because they represent amounts after fewer half-lives or assume complete decay.
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