1. How many ATOMS of sulfur are present in 2.25 moles of sulfur trioxide ? ____ atoms of sulfur. 2. How many MOLES of oxygen are present in 1.01×1023 molecules of sulfur trioxide ? ___moles of oxygen. Solution Ans. #1. 1 mol SO 3 consists of 1 S-atoms. So, moles of S in SO 3 = 2.25 mol Now, Number of S-atoms = Moles of S x N A = 2.25 mol x (6.022 x 10 23 atoms/ mol) = 1.355 x 10 24 atoms #2. Moles of SO 3 = Number of SO 3 molecules / N A = 1.01 x 10 23 molecule / (6.022 x 10 23 molecules / mol) = 0.1677 mol # 1 SO 3 molecule consists of 3 O-atoms. So, Moles of O = 3 x Moles of SO 3 = 3 x 0.1677 mol = 0.5032 mol .