Final answer:
The amount of iodine-131 left after 24 days can be calculated using the half-life. A total of 1.25mg is left.
Step-by-step explanation:
The half-life of iodine-131 is 8 days. This means that every 8 days, the amount of iodine-131 is reduced by half. The formula for calculating the amount left after a certain period of time is:
Amount left = Initial amount * (1/2)^(time elapsed / half-life)
In this case, the initial amount is 10mg and the time elapsed is 24 days. Plugging these values into the formula, we get:
Amount left = 10mg * (1/2)^(24 / 8)
= 10mg * (1/2)^3
= 10mg * (1/8)
= 1.25mg
Therefore, the answer is A. 1.25mg.