Answer
$N_o = 6.3 \times 10^{18}$
Work Step by Step
To find the number of plutonium absorbed, use the equation
$N_o = \frac{m}{M_{Pu}} N_A$
$N_o = \frac{2.5 \times 10^{-3} g}{239 g/u} (6.02 \times 10^{23} /mol)$
$N_o = 6.3 \times 10^{18}$