Answer
$7.6\times 10^{-21}\ g\ Xe $
Work Step by Step
1. Use Avogadro's number and the molar mass of xenon as conversion factors in order to determine the mass of the xenon atoms.
2. $35\ atoms\ Xe\times\frac{1\ mol\ Xe}{6.022\times 10^{23}\ atoms\ Xe}\times\frac{131.3\ g \ Xe}{1\ mol\ Xe} = 7.6\times 10^{-21}\ g\ Xe $
