Question

what mass of Fe3O4 would conatin 1.85*10^21 atoms of Fe?

Answer 1

1.85E21 atoms Fe/3 = ? molecules Fe3O4.

?molecules Fe3O4 x (1/6.02E23) = ? mols Fe3O4.
? mols Fe3O4 x (molar mass Fe3O4/1 mol) = grams Fe3O4.