# Question #5ef03

$24 g E u$
If the half-life of the $E u$ nuclide is $13 y$, and time given is $26 y$, there are $\frac{26}{13} = 2$ half-lives in the time interval. That is, the mass of the $E u$ nuclides will decrease by $\frac{1}{2}$ twice and thus decrease by a factor of $\frac{1}{4}$.
$\frac{1}{4} \times 96 g = 24 g$