How many O2 molecules are needed to react with 7.06 g of S? Express your answer numerically in units of molecules.?

Molar mass of S = 32.06 g/mol
No. of moles of S = (7.06 g) / (32.1 g/mol) = 0.220 mol

S + O₂ → SO₂
Mole ratio S : O₂ = 1 : 1
No. of moles of O₂ = No. of moles of S = 0.220 mol

Avogadro constant = 6.022 × 10²³ /mol
No. of O₂ molecules = (0.220 mol) × (6.022 × 10²³ O₂ molecules/mol) = 1.32 × 10²³ O₂ molecules


OR:
(7.06 g S) × (1 mol S / 32.1 g) × (1 mol O₂ / 1 mol S) × (6.022 × 10²³ O₂ molecules / 1 mol O₂) = 1.32 × 10²³ O₂ molecules

It depends on which oxide of S you're making. Supposing it is SO2:
S + O2 → SO2 [balanced as written]

(7.06 g S) / (32.0655 g S/mol) × (1 mol O2 / 1 mol S) × (6.022 × 10^23 molecules/mol) =
1.33 × 10^23 molecules O2