The Half-Life of Cobalt-60 Is $5.3$ Years, While That of Strontium-90 Is About 29 Years

Multiple Choice

The half-life of cobalt-60 is $5.3$ years, while that of strontium-90 is about 29 years. Suppose you have samples of both isotopes, and that they initially have the same activity (number of decays per second) . What must be true of the numbers of cobalt-60 and strontium-90 nuclei in these samples?

A) There are more strontium-90 than cobalt-60 nuclei.
B) There are more cobalt-60 than strontium-90 nuclei.
C) There are equal numbers of cobalt-60 and strontium-90 nuclei.
D) It is not possible to compare numbers of nuclei without knowing the masses of the samples.