Answer:
This type of reaction almost always produces a gas. The following are examples of decomposition reactions: Heating mercury (II) oxide produces oxygen gas: 2HgO (s) → 2Hg (l) + O2 (g). Leaving the cap off the carbonated soft drink bottle allows the carbonic acid to release carbon dioxide: H2CO3 (aq) → H2O (l) + CO2 (g). Hope this helps :)