Problem

t = 0

, the number of radioactive nuclei of a radioactive substance is

x

and its radioactivity is

y

. The half-life of the radioactive substance is

T

. Then, a.

\frac{x}{y}

is constant throughout b.

\frac{x}{y} > T

c. value of

xy

remains half after one half-life d. value of

xy

remains one fourth after one half-life