Answer :
1. Set up conversion factors.
92.8 mg x 1 g/10^3 mg x 1 mol/28.09 g x 6.022x10^23 atoms/1 mol
2. Cancel units.
1.99 x 10^21 Si atoms
92.8 mg x 1 g/10^3 mg x 1 mol/28.09 g x 6.022x10^23 atoms/1 mol
2. Cancel units.
1.99 x 10^21 Si atoms