Answer is: in chemical reaction with with weak acid, sodium carbonate produce carbonic acid (H₂CO₃), which decomposes into carbon(IV) oxide (fizzy bubbles) and water.
Balanced chemical reaction:
Na₂CO₃ + 2HClO → CO₂(g) + H₂O + 2NaClO.
Chemical decomposition is the separation of a carbonic acid into water and carbon dioxide: H₂CO₃ → CO₂ + H₂O.
