Answer:
Carbon dioxide (CO₂)
Explanation:
Carbonic acid decomposes to release water and carbon dioxide:
H₂CO₃ → H₂O + CO₂
In an aqueous solution, it has this two equilibriums where it release 2 protons. It is a weak acid:
H₂CO₃ + H₂O ⇄ HCO₃⁻ + H₃O⁺ Ka₁
HCO₃⁻ + H₂O ⇄ CO₃⁻² + H₃O⁺ Ka₂
