Dead burnt plaster is

Correct answer: 1)

Concept:

• Plaster of Paris (CaSO4 ·½ H₂O) is a hemihydrate of calcium sulphate.
• Plaster is generally made up of calcium sulphate which is basically used to make pots, chalks, and other decorative items rather than this the main basic use of plaster is in medical use i.e. to fix fractured bones.

Explanation:

• Plaster of Paris is obtained when gypsum, CaSO₄ ·2H₂O, is heated to 393 K.
• 2CaSO₄ ·2H₂O → 2(CaSO₄)·H₂O + 3H₂O.
• Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO4 is formed, known by the name anhydrite.
• It’s called dead burnt because it doesn’t set like the plaster of Paris when wet with water.
• Dead burnt plaster is produced which is known as anhydrite or anhydrous calcium sulphate is generally have to start the product gypsum which is represented by the chemical formula CaSO₄.
• It has a remarkable property of setting with water.
• On mixing with an adequate quantity of water it forms a plastic mass that gets into a hard solid in 5 to 15 minutes. 

Conclusion:

Thus, Dead burnt plaster is CaSO4

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