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 parent 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 parent isotope will have halved three times. Starting with 72 grams, after one half-life it would be 36 grams, after two half-lives it would be 18 grams, and after three half-lives it would be 9 grams.

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