The percentage of sulfur in chalcopyrite (CuFeS₂) can be calculated by determining the mass of sulfur present in the compound relative to its total mass. Here's the calculation:

Molar Mass of Chalcopyrite (CuFeS₂) = 64 (Copper) + 56 (Iron) + 32 x 2 (Sulfur)

Molar Mass = 64 + 56 + 64 = 184 g/mol

Mass of Sulfur in Chalcopyrite = 2 x 32 g/mol (Since there are two sulfur atoms in the compound) = 64 g/mol

Percentage of Sulfur in Chalcopyrite = (Mass of Sulfur / Molar Mass of Chalcopyrite) × 100

Percentage of Sulfur = (64 g/mol / 184 g/mol) × 100 ≈ 34.78%

Therefore, the percentage of sulfur in chalcopyrite is approximately 34.78%.