If an Isotope's Half-Life is 100 Years

Question

If an isotope's half-life is 100 years,
A) in 50 years, only half of the atoms in a sample of that isotope will remain.
B) in 100 years, only half of the atoms in a sample of that isotope will remain.
C) in 200 years, only half of the atoms in a sample of that isotope will remain.
D) that isotope will no longer exist in 200 years.
E) that isotope will no longer exist in 50 years.

Accepted Answer

Half-life is the time it takes for half of the atoms in a sample of a radioactive substance to decay. So, after one half-life, half of the original sample will remain, and after two half-lives, only one-fourth of the original sample will remain. Therefore, after 100 years (which is one half-life for this particular isotope), only half of the atoms in a sample of that isotope will remain.