Answer
0.0779 g SO₃
Procedure
To solve this question, you will need to use the Avogadro's number equivalent to 6.02214 x 10^23 molecules/ mol, and then the molecular weight in grams per mole for the SO₃.
[tex]5.86\times10^{20}\text{ molecules SO}_3\frac{1\text{ mol SO}_3}{6.02214\text{ x 10}^{23}\text{molecules SO}_3}\frac{80.06\text{ g SO}_3}{1\text{ mol SO}_3}=0.0779\text{ g SO}_3[/tex]