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

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."