The correct option is Washing soda.
Explanation
Chemical compounds often possess common names used in industrial and household contexts, distinct from their IUPAC nomenclature. The compound $Na_2CO_3 \cdot 10H_2O$ is chemically known as Sodium Carbonate Decahydrate.
Option Analysis:
- Washing soda Washing soda: Correct. Washing soda is the common name for Sodium Carbonate Decahydrate ($Na_2CO_3 \cdot 10H_2O$). It is a basic salt used extensively in glass, soap, and paper industries, and for removing permanent hardness of water.
- Caustic soda Caustic soda: Incorrect. Caustic soda is the common name for Sodium Hydroxide ($NaOH$), a strong base used in manufacturing soap and paper.
- Soda water Soda water: Incorrect. Soda water refers to carbonated water, which is water containing dissolved carbon dioxide gas under pressure. It is not a salt compound.
- Bleaching powder Bleaching powder: Incorrect. Bleaching powder is chemically Calcium Oxychloride ($CaOCl_2$), produced by the action of chlorine on dry slaked lime.
Key Takeaway:
Washing soda is Sodium Carbonate Decahydrate ($Na_2CO_3 \cdot 10H_2O$), whereas Baking soda is Sodium Hydrogen Carbonate ($NaHCO_3$).