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PCAT Review Questions - Pharmacy College

Category - Chemistry

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A 40.0 gram sample of a radioactive element decays to 5.0 grams in 15 hours. What is the half-life of this element?
  1. 3 hours
  2. 2 hours
  3. 6 hours
  4. 7.5 hours
  5. 5 hours
Explanation
Answer: 5 hours

In 15 hours, this substance has decayed to 1/8 of its original mass. In other words, the substance has progressed through three half-lives (1/2 x 1/2 x 1/2 = 1/8). Thus, a single-half life for this substance is 5 hours.
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