In the reaction between sodium carbonate and hydrochloric acid, which gas is released?

• A. O2
• B. H2
• C. NH3
• D. CO2

Answer: (D)

Acid reacting with a carbonate releases carbon dioxide gas. When sodium carbonate meets hydrochloric acid, the carbonate reacts with the hydrogen ions to form carbonic acid, which quickly decomposes to carbon dioxide and water. The balanced equation shows the products as sodium chloride, carbon dioxide, and water: Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O. The CO2 escapes as fizzing bubbles, showing gas evolution. The other gases listed aren’t produced in this reaction because there’s no pathway in this combination to form O2, H2, or NH3; the reaction specifically yields salt, water, and carbon dioxide.