Answer: A — Washing Soda
Washing Soda (Na₂CO₃·10H₂O) is used in the glass, soap, and paper industries, as well as for softening hard water.
This is from the Acids, Bases and Salts chapter (Chapter 2). Examiners expect you to recall the uses of washing soda specifically — glass, soap, paper industries, and water softening. Do not confuse it with Baking Soda (NaHCO₃), which is used in cooking and as an antacid. The source passages provided are from Chapter 4 and do not cover this topic, but the correct answer is firmly from the CBSE syllabus Chapter 2.