Two samples P and Q of the same radioactive isotope initially contain different numbers of nuclei. Separate plots of lnN versus time for the two samples are straight lines that are parallel to each other. Which one of the following conclusions is correct?
(a) The sample whose lnN–time plot has the higher intercept must possess a shorter half-life.
(b) The half-lives of P and Q are equal because the slopes of their lnN versus time plots are the same.
(c) The decay constants of P and Q are different since their intercepts on the lnN axis are different.
(d) The half-life of a radioactive sample gradually decreases as the number of undecayed nuclei falls with time.