Here's how to calculate the percent sulfur in sulfur dioxide (SO₂):

1. Find the molar mass of sulfur dioxide (SO₂):

* Sulfur (S): 32.06 g/mol

* Oxygen (O): 16.00 g/mol (and we have two oxygen atoms)

* Total molar mass of SO₂: 32.06 + (16.00 x 2) = 64.06 g/mol

2. Calculate the mass percentage of sulfur:

* (Mass of sulfur / Molar mass of SO₂) x 100%

* (32.06 g/mol / 64.06 g/mol) x 100% = 50.04%

Therefore, sulfur dioxide (SO₂) is approximately 50.04% sulfur by mass.