Why do baking soda and vinegar bubble when mixed?

Answer: The acid reacts with baking soda and produces carbon dioxide

The acid reacts with baking soda and produces carbon dioxide ✓ — Vinegar’s acetic acid reacts with sodium bicarbonate in baking soda, producing carbon dioxide gas along with water and sodium acetate. The newly formed gas escapes as bubbles; it was not simply hiding in the liquid.

Stirring releases air that was already trapped in the liquid — Releasing trapped air cannot account for the sustained fizzing. The ingredients react and make new carbon dioxide molecules, so bubbles can form even without vigorous stirring.

The mixture heats up until the liquid begins to boil — The fizz is not boiling caused by a temperature rise. Mixing ordinary vinegar and baking soda usually cools the mixture overall because the process absorbs heat. The bubbles are carbon dioxide produced by the reaction.