Why does baking soda make things rise?

Answer: Releases CO2 gas when heated

Releases CO2 gas when heated ✓ — Correct! Baking soda (sodium bicarbonate) is a base that reacts with acids (buttermilk, vinegar, lemon juice) or heat to produce carbon dioxide gas. The CO2 bubbles get trapped in batter, making it rise and creating fluffy texture. Chemical equation: NaHCO3 → Na2CO3 + H2O + CO2. That's chemical leavening!

Absorbs moisture and expands — Wrong. Baking soda doesn't expand from moisture. It chemically reacts to produce gas bubbles that leaven baked goods.

Heat expands trapped air — Wrong. While air does expand when heated, that alone doesn't cause significant rise. Baking soda releases CO2 gas when it reacts with acid, creating new gas bubbles that make batter rise.