Final answer:
The original sample size of I-131 was 200 grams.
Step-by-step explanation:
The half-life of I-131 is 8 days. After 24 days, there are 25 g of I-131 remaining. To find the original sample size, we need to determine how many half-lives occurred in 24 days. 24 days / 8 days per half-life = 3 half-lives. Each half-life reduces the sample size by half. So, starting with 25 g, we can work backwards to find the original sample size: 25 g x 2^(3 half-lives) = 200 g. Therefore, the original sample size was 200 grams. Option 3, 200 grams, is the correct answer.