Question

P-32, a radioisotope used to treat leukemia, has a half-life of 14.3 days. If a sample contains 8.0 mg of P-32, how many milligrams of P-32 remain after 42.9 days?

a) 0.50 mg
b) 1.0 mg
c) 2.0 mg
d) 4.0 mg

Answer 1

After 42.9 days, 25% of the original sample of P-32 remains.

Step-by-step explanation:

The half-life of P-32 is 14.3 days. This means that after 14.3 days, half of the sample will have decayed. After another 14.3 days (a total of 28.6 days), half of the remaining sample will have decayed again. After a total of 42.9 days (3 half-lives), only 25% of the original sample will remain.

Given that the original sample contains 8.0 mg of P-32, the amount of P-32 remaining after 42.9 days is 25% of 8.0 mg, which is 2.0 mg. Therefore, the correct answer is c) 2.0 mg.