A rock sample containing an isotope with a half-life of 12 million years has an initial mass of 72 grams. How much of the daughter isotope will be present after three half-lives?
A)4.5 grams
B)9 grams
C)18 grams
D)54 grams
E)63 grams

Question

Quizplus · Accepted Answer

After three half-lives, the mass of the original isotope will have halved three times: from 72 grams to 36 grams, then to 18 grams, and finally to 9 grams. This means 63 grams (72 - 9) have been converted into the daughter isotope.

A Rock Sample Containing an Isotope with a Half-Life of 12