Isotope R has a half-life of 2.0h, whereas isotope S has a half-life of 8.0h. A sample initially contains equal numbers of atoms of R and S. Which statement correctly compares the numbers of atoms of R and S remaining after 16h?
a) Fewer atoms of R remain because R has undergone eight half-lives, whereas S has undergone only two
b) Fewer atoms of R remain because R has undergone four half-lives while S has undergone only two
c) More atoms of R remain because the shorter half-life means it decays more slowly than S
d) Fewer atoms of S remain because S has undergone eight half-lives, whereas R has undergone only two