Question

Dead burn plaster is
(a) CaSO₄.2H₂O
(b) MgSO₄. 7H₂O
(c) CaSO₄.½ H₂O
(d) CaSO₄

Answer 1

Option D) CaSO is called dead burnt plaster since it is void of water molecules

Answer 2

Option a

Reason : Plaster of Paris is prepared by heating gypsum at 120° C.
2CaSO4.2H2O → (CaSO4)2.H2O + 3H2O 
  Gypsum        Plaster of Paris   

On heating plaster of Paris at 200°C, it forms anhydrous calcium sulphate, i.e., dead plaster which has no setting property as it absorbs water very slowly.