Concept:Fermentation is a chemical process where microorganisms break down organic substances, producing gases that make Dhokla spongy.Explanation:Dhokla batter is made from rice and split chickpeas. Sour curd or baking soda is added to trigger fermentation. Bacteria and yeasts act on the batter, releasing carbon dioxide. This creates air pockets, giving Dhokla its light, fluffy texture. Fermentation is used in making bread, yogurt, and vinegar.Answer:The correct option is C. fermentation.