CaSO₄.1/2H₂O.This is the chemical formula of plaster of Paris and when it is added to water it converts into gypsum. which can be written like this:
CaSO₄.1/2H₂O+1 1/2H₂O⇄CaSO₄.2H₂O.the gypsum on heating again converts into gypsum which is depicted by symbol ⇄ meaning interchangeable.
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SUGGEST FOR EDITION.