Which proportion of a radioactive isotope is expected to remain in an unaltered (unreacted)state after the passage of three half-lives?
A)one-third
B)three-halves
C)one-eighth
D)one-sixth

Question

Quizplus · Accepted Answer

After the passage of one half-life, half of the original isotope will remain. After two half-lives, half of that remaining half will remain, which is one-fourth of the original isotope. After three half-lives, half of that remaining one-fourth will remain, which is one-eighth of the original isotope. Therefore, the proportion expected to remain in an unaltered state after the passage of three half-lives is one-eighth.

Which Proportion of a Radioactive Isotope Is Expected to Remain