Multiple choice What happens when a liquid boils? It heats up. The liquid disappears. A chemical reaction is happening. Bubbles of gas form inside the liquid. Reveal answer Fill a bubble to check yourself D Correct answer Explanation Boiling is a physical change where a liquid turns into a gas throughout the entire volume of the liquid, not just at the surface. This rapid phase change causes bubbles of vapor to form within the liquid and rise to the top.