If a rock started with 1,000 atoms of a parent but now contains 250 atoms, how many half lives have passed?
A) .25 half lives
B) .5 half lives
C) 1 half life
D) 2 half lives
E) there is no way to tell

Question

Quizplus · Accepted Answer

With each half-life, the amount of the parent atoms halves. Starting with 1,000 atoms and ending with 250 means it has 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