Answer
.8 mmol
Work Step by Step
We know that the given compound has a molar mass of 318.12 g/mol. Since we also know that there are .250 grams present in the sample, we obtain:
$$\frac{1 mol}{318.12 g}* \frac{.250 g}{1}=.8 \times 10^{-3} mol = .8 \ mmol $$
