The half-life of iron-59 is 45 days. After three months, how much of a 72-gram sample of iron-59 is left?

Question

Quizplus · Accepted Answer

First, we need to find out how many half-lives have passed in three months:

1 half-life = 45 days 
3 months = 90 days

90 days / 45 days per half-life = 2 half-lives

So, after 2 half-lives, the amount of iron-59 remaining is:

1/2 x 1/2 = 1/4

So, the amount remaining is:

72 grams x 1/4 = 18 grams

Therefore, the answer is B, 18 grams.

The Half-Life of Iron-59 Is 45 Days