The chemicals used in making fire extinguisher are acid (Sulphuric acid) and Sodium hydrogen carbonate (NaHCO₃). This acid reacts with sodium hydrogen carbonate and CO₂ gas evolves. And this CO₂ gas helps to put off the fire.

H₂SO₄ + 2NaHCO₃ → 2CO₂ +2 H₂O + Na₂SO₄