Which gas is used by chemical leaveners, such as baking powder and baking soda, to lighten and aerate baked goods?

Carbon dioxide

The correct answer is option 2. Carbon dioxide.

Chemical leaveners, such as baking powder and baking soda, release carbon dioxide gas during the baking process, contributing to the leavening or rising of baked goods. Here's an explanation:

1. Baking Soda (Sodium Bicarbonate): Baking soda is a common chemical leavener used in baking. It is a white crystalline powder with the chemical formula \( \text{NaHCO}_3 \). When baking soda is mixed with an acidic ingredient (such as vinegar, buttermilk, or yogurt) and exposed to heat, it undergoes a chemical reaction. The acid reacts with baking soda to produce carbon dioxide gas, water, and a salt.

\[ \text{NaHCO}_3 + \text{acid} \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{salt} \]

2. Baking Powder: Baking powder is a leavening agent that contains both an alkaline substance (usually baking soda) and an acid (such as cream of tartar). Some baking powders are "double-acting," meaning they release carbon dioxide gas at two different stages: when mixed with liquid and when exposed to heat during baking. The first reaction occurs when the baking powder is mixed with a liquid, producing carbon dioxide. The second reaction takes place during baking when heat is applied.

\[ \text{NaHCO}_3 + \text{acid} \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{salt} \]

3. Carbon Dioxide \((CO_2)\) Production:

The carbon dioxide gas produced during these reactions gets trapped in the dough or batter, creating bubbles and causing the mixture to rise or expand. The expansion of the dough or batter results in a lighter, fluffier texture in the final baked goods.

In summary, carbon dioxide gas is the key agent responsible for leavening in baked goods when using chemical leaveners like baking soda and baking powder. The gas produced during the chemical reactions creates bubbles, leading to the characteristic light and airy texture in cakes, muffins, and other baked items.