Final answer:
When seashells are immersed in vinegar, a chemical reaction occurs that results in the release of carbon dioxide gas, causing fizzing.
Step-by-step explanation:
When seashells, which are made up of calcium carbonate, are immersed in vinegar (which contains acetic acid), a chemical reaction occurs.
The acetic acid reacts with the calcium carbonate, resulting in the formation of carbon dioxide gas, water, and calcium acetate.
This reaction can be represented by the following equation:
CaCO3 + 2CH3COOH → CO2 + H2O + Ca(CH3COO)2
The release of carbon dioxide gas during the reaction is what causes the fizzing observed when seashells are immersed in vinegar.