The additional product formed when an acid is neutralized by an antacid containing a carbonate or bicarbonate is carbon dioxide (CO2).

Here's why:

* Carbonates (CO3^2-) and bicarbonates (HCO3-) react with acids to produce carbon dioxide gas, water, and a salt.

* Example:

* Sodium bicarbonate (NaHCO3) reacts with hydrochloric acid (HCl) to form sodium chloride (NaCl), water (H2O), and carbon dioxide (CO2):

NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)

The release of carbon dioxide is the reason why you often feel a fizzy sensation after taking an antacid containing carbonates or bicarbonates.