Iodine-131 has a half-life of 8.0 minutes. How many half-lives will pass in 120 minutes?

• A. 15
• B. 10
• C. 12
• D. 8

Answer: (A)

Verified step by step guidance

1. Identify the given information: the half-life of iodine-131 is 8.0 minutes, and the total time elapsed is 120 minutes.
2. Recall the formula to find the number of half-lives passed: \(\text{Number of half-lives} = \frac{\text{Total time elapsed}}{\text{Half-life}}\).
3. Substitute the given values into the formula: \(\text{Number of half-lives} = \frac{120}{8.0}\).
4. Perform the division to find how many half-lives have passed (do not calculate the final number here, just set up the expression).
5. Interpret the result as the number of times the iodine-131 sample has undergone decay by half during the 120 minutes.