1. The problem asks for the gas produced when propanoic acid reacts with calcium trioxocarbonate(IV). 2. Calcium trioxocarbonate(IV) is another name for calcium carbonate, CaCO3. 3. The reaction between a carboxylic acid (like propanoic acid, C2H5COOH) and calcium carbonate produces a salt, water, and carbon dioxide gas. 4. The general reaction is: $$\text{2 RCOOH} + \text{CaCO}_3 \rightarrow \text{(RCOO)}_2\text{Ca} + \text{H}_2\text{O} + \text{CO}_2$$ where RCOOH is the carboxylic acid. 5. For propanoic acid, R = C2H5, so the reaction is: $$\text{2 C}_2\text{H}_5\text{COOH} + \text{CaCO}_3 \rightarrow \text{(C}_2\text{H}_5\text{COO)}_2\text{Ca} + \text{H}_2\text{O} + \text{CO}_2$$ 6. The gas given off is carbon dioxide, $$\text{CO}_2$$. Final answer: The gas produced is carbon dioxide ($$\text{CO}_2$$).