How many molecules are in 3.5 g of sulfur dioxide

6.02*10^23 molecules

Turn the grams of sulfur dioxide into moles:

3.5 g • 1 mol/64.07 g SO2 = 0.05463 mol

Then multiply it by 6.02 • 10^23:

0.05463 mol • 6.02 • 10^23 = 3.289 • 10^22 molecules

3.3 • 10^22 molecules