There are two iron atoms and three oxygen atoms in each molecule of Fe2O3. So that's five atoms per molecule.One mole of any molecular substance contains 6.02×1023 molecules. Since there are two iron atoms in each of the molecules we're considering, there will be (6.02×1023)⋅2=1.204×1024 iron atoms in a whole mole of them.But we're considering 0.550 mol, so multiply by 0.550:n=(0.550 mol)⋅(3.01×1024 atoms/mol)=6.62×1023 iron atoms.
