Which of the following chemical equations is balanced?
1) Fe₂O₃ + CO → Fe + 2CO₃
2) CuO + 2NH₃ → 3Cu + 3H₂O
3) N2 + 4Al + 3Fe₃O₄ → 4Al₂O₃ + 9Fe
4) Na₂SO₂ + S → S₂O₃ + S