Which of the following makes bread soft and spongy when baking soda is

Which of the following makes bread soft and spongy when baking soda is added?

Sodium salt of acid
NaHCO₃
CO₂
H₂O
This question was previously asked in
UPSC CAPF – 2022
The correct answer is C, CO₂.
Baking soda is sodium bicarbonate (NaHCO₃). When used in baking, it acts as a leavening agent.
In the presence of heat or an acidic ingredient (like those often found in dough or baking powder), baking soda undergoes a chemical reaction that produces carbon dioxide (CO₂) gas.
The main reactions are:
1. Decomposition by heat (slow without acid): 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(g) + CO₂(g)
2. Reaction with an acid (e.g., citric acid, tartaric acid, or acids in buttermilk/yogurt): NaHCO₃(s) + H⁺(aq) → Na⁺(aq) + H₂O(l) + CO₂(g)
The carbon dioxide gas gets trapped within the gluten matrix of the dough, causing it to expand and rise. This creates small air pockets, which give the bread or cake a light, fluffy, soft, and spongy texture.
While NaHCO₃ is the source of the leavening action, it is the carbon dioxide gas produced from its reaction or decomposition that physically causes the dough to rise and become soft and spongy. Sodium carbonate (Na₂CO₃), formed from heat decomposition, can leave a slightly soapy taste if not neutralized by an acid.