How does the length of time soda is left out affect its fizziness?

The length of time soda is left out affects its fizziness due to the gradual release of carbon dioxide gas, which is responsible for carbonation. When soda is exposed to air, the pressure inside the container decreases, allowing carbon dioxide to escape more rapidly. As time passes, more gas is lost, resulting in a flatter taste and reduced fizziness. Therefore, the longer soda is left open, the less carbonated it becomes.