Final answer:
The mass fraction of sulfur in zinc sulfide is 32.9% by mass, calculated by subtracting the mass percentage of zinc from 100%.
Step-by-step explanation:
If zinc sulfide is 67.1% zinc by mass, we can determine the mass fraction of sulfur in zinc sulfide by subtracting the mass percentage of zinc from 100%. Since the remainder must be sulfur (assuming no impurities), we calculate the mass fraction of sulfur as:
100% - 67.1% = 32.9%
Therefore, the mass fraction of sulfur in zinc sulfide is 32.9% percent by mass. To put this into perspective, for every 100 grams of zinc sulfide, 32.9 grams would be sulfur.