Question

The half-life of I-131 is 8 days. If 25 g are left after 24 days, how many grams are in the original sample?

Option 1: 100 grams
Option 2: 50 grams
Option 3: 200 grams
Option 4 : 400 grams

Answer 1

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.