Isotope X has a decay constant that is twice the decay constant of isotope Y. Which one of the following correctly compares their half-lives?
a) Half-life of X is double the half-life of Y.
b) Half-life of X is half the half-life of Y.
c) Half-life of X is approximately 0.35 times the half-life of Y.
d) The half-lives cannot be compared without knowing the initial number of nuclei.