Which gas is produced when an acid reacts with a carbonate?

When an acid reacts with a carbonate, the primary product of this reaction is carbon dioxide. This process typically follows the general reaction formula where an acid (such as hydrochloric acid) interacts with a carbonate (like calcium carbonate). During this reaction, the carbonate reacts with the hydrogen ions from the acid, resulting in the release of carbon dioxide gas, water, and a salt.

For example, with hydrochloric acid:

[ \text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2 \uparrow ]

The upward arrow indicates that carbon dioxide is released as a gas. This is the classic demonstration often shown in chemistry labs, where effervescence (bubbles) occurs due to the production of carbon dioxide, which can be observed in real-time during the reaction.

In contrast, gases like oxygen, nitrogen, or hydrogen are not typically produced in reactions between acids and carbonates. These gases may result from different chemical processes, not from the acid-carbonate reaction. Thus, the specific reaction between an acid and a carbonate distinctly produces carbon dioxide, making it the correct choice in this scenario.