Question SPM.1A.SL.TZ0.23

Two radioactive samples $\mathrm{X}$ and $\mathrm{Y}$ have the same half-life. Initially the ratio $\frac{\mathrm{activity} \mathrm{of} \mathrm{X}}{\mathrm{activity} \mathrm{of} \mathrm{Y}}$ is 4.

What is this ratio after 2 half-lives?

A.  $\frac{1}{2}$

B.  1

C.  2

D.  4