Baking soda is _____.

sodium hydrogencarbonate

The correct answer is option 3. sodium hydrogencarbonate.

Baking soda, chemically known as sodium hydrogen carbonate or sodium bicarbonate, has the chemical formula \( NaHCO_3 \). It is a white crystalline powder that is commonly used in baking as a leavening agent. Here's the explanation:

1. Sodium Hydrogen Carbonate \((NaHCO_3)\):  The chemical name "sodium hydrogen carbonate" indicates its composition. It consists of sodium ions (\(Na^+\)), hydrogen ions (\(H^+\)), and bicarbonate ions (\(HCO_3^-\)).

2. Leavening Agent: In baking, baking soda serves as a leavening agent, which means it helps dough or batter rise by releasing carbon dioxide gas when it reacts with acids or acidic ingredients. The production of carbon dioxide gas creates bubbles in the mixture, leading to a light and fluffy texture in baked goods.

3. Acid-Base Reaction: When baking soda reacts with an acid, such as vinegar, buttermilk, or yogurt, it undergoes an acid-base reaction. The reaction can be represented as follows:

\[ NaHCO_3 + \text{Acid} \rightarrow \text{Carbon dioxide gas} + \text{Water} + \text{Salt} \]

For example, when baking soda reacts with vinegar, it produces carbon dioxide gas, water, and sodium acetate.

4. Common Household Uses: Baking soda is not only used in baking but also has various household uses. It is often used as a cleaning agent, deodorizer, and for various other practical purposes.

In summary, baking soda is the common name for sodium hydrogen carbonate, and its ability to release carbon dioxide gas makes it a versatile ingredient in both baking and household applications.