1. Write the balanced chemical equation:

S(s) + O₂(g) → SO₂(g)

2. Determine the mole ratio:

The balanced equation shows that 1 mole of sulfur reacts with 1 mole of oxygen to produce 1 mole of sulfur dioxide.

3. Apply Avogadro's Law:

Avogadro's Law states that equal volumes of gases at the same temperature and pressure contain the same number of molecules (and therefore moles). Since we're dealing with gases at the same conditions, we can use the volume ratio directly.

4. Calculate the volume of oxygen:

Since the mole ratio of oxygen to sulfur dioxide is 1:1, the volume of oxygen needed is the same as the volume of sulfur dioxide produced.

Therefore, you need 3.5 L of oxygen to react with the solid sulfur and form 3.5 L of SO₂.