UPSC NDA I 2021 General Ability Solved Paper

The correct answer is Plaster of Paris.
Key Points
- Preparation of Plaster of Paris doesn't require the use of NaCl.
- It is simply obtained by heating gypsum (CaSO.2H O) at 120∘C in a rotary kiln. - Reaction involved: 2(CaSO4⋅2H2O)⟶2(CaSO4)⋅H2O+2H2O.
‌ (Gypsum) ‌&‌ (Plaster of Paris) (Water) ‌
- It turns in solid mass when mixed with water and hence used for plasterwork.