Answer:
90.2 da
Explanation:
The half-life of iron-59 (45.1 da) is the time it takes for half the Fe to decay.
After one half-life, half (50 %) of the original amount will remain.
After a second half-life, half of that amount (25 %) will remain, and so on.
We can construct a table as follows:
No. of Time Percent Fraction
half-lives days remaining remaining
1 45.1 50 ½
2 90.2 25 ¼
3 135 12.5 ⅛
4 180 6.25 ¹/₁₆
We see that 25 % remains after two half-lives or 90.2 da.
