1. Determine the molar mass of sulfur trioxide (SO3):

* Sulfur (S): 32.06 g/mol

* Oxygen (O): 16.00 g/mol (x 3 = 48.00 g/mol)

* Total molar mass of SO3: 32.06 + 48.00 = 80.06 g/mol

2. Calculate the moles of SO3:

* Moles = mass / molar mass

* Moles of SO3 = 9.96 g / 80.06 g/mol = 0.1244 mol

3. Determine the moles of sulfur atoms:

* The chemical formula SO3 shows that there is 1 sulfur atom per molecule of SO3.

* Therefore, the moles of sulfur atoms are equal to the moles of SO3: 0.1244 mol

4. Convert moles of sulfur to atoms:

* Avogadro's number: 6.022 x 10^23 atoms/mol

* Atoms of sulfur = moles of sulfur * Avogadro's number

* Atoms of sulfur = 0.1244 mol * 6.022 x 10^23 atoms/mol = 7.49 x 10^22 atoms

Therefore, there are approximately 7.49 x 10^22 atoms of sulfur present in 9.96 grams of sulfur trioxide.