How many o2 molecules are needed to react with 3.92 g of s?

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

a corroding iron, if that's one of your choices