Answer
There will around $4.9$ grams left out of the 30-gram sample after 250 years.
Work Step by Step
This is about half-life so it involves exponential decay.
RECALL:
Exponential decay is represented by the formula
$y=C(1-r)^x$
where
C = initial/original amount
r = decay rate
x = number of time intervals
The given situation has:
C = 30 grams
r = $50\%$ per 96 years
x = $\frac{250}{96} = \frac{125}{48}$
Substitute these values into the given formula above to have:
$y=30(1-50\%)^{\frac{125}{48}}
\\y=30(1-0.5)^{\frac{125}{48}}
\\y=30(0.5^{\frac{125}{48}})
\\y \approx 4.9$
