If a rock started with 1,000 atoms of a parent but now contains 250 atoms,how many half-lives have passed?
A)0.25 half-lives
B)0.5 half-lives
C)2 half-lives
D)4 half-lives
E)There is no way to tell.

Question

Quizplus · Accepted Answer

Each half-life reduces the number of parent atoms by half. Starting with 1,000 atoms and ending with 250 means the amount has been halved twice (1,000 to 500 to 250), indicating 2 half-lives have passed.

If a Rock Started with 1,000 Atoms of a Parent