You need 7.36 × 10²² molecules of O₂ to react with 3.92 g of S.
Balanced equation: S + O₂ → SO₂
Moles of S = 3.92 g S × (1 mol S/32.06 g S) = 0.1223 mol S
Moles of O₂ = 0.1223 mol S × (1 mol O₂/1 mol S) = 0.1223 mol O₂
Molecules of O₂ = 0.1223 mol O₂ × (6.022 × 10²³ molecules O₂/1 mol O₂)
= 7.36 × 10²² molecules O₂
