How many moles of oxygen gas would be needed to completely burn 8 moles of
hydrogen sulfide?

12 mol of O2

Reason being is because of this equation. Hope you understand this.

Equation: 2 H2s (g) + 3 o2 (g) + 2 SO2 (g) + 2 H2O (g)

Before: 8 mol   xs mol    0 mol     0 mol

Change: -8 mol   -12 mol   +8 mol   +8 mol

After: 0 mol   XS mol   +8 mol   +8 mol

So therefore, your answer is 12 mol. Hope this helps and please mark brainliest if this truly and deeply helped you. Stay safe and have a nice day or night!