A) oxidation with atmospheric oxygen
B) Combination with atmospheric \[C{{O}_{2}}\]
C) dehydration
D) hydration to yield another hydrate
Correct Answer: D
Solution :
Setting of plaster of parts is due to hydration. During hydration, it takes up the water of crystallisation and converted into dihydrate. This further sets into hard mass. \[\underset{Plaster\,\,of\,\,Paris}{\mathop{CaS{{O}_{4}}.\frac{1}{2}{{H}_{2}}O}}\,\xrightarrow{{{H}_{2}}O}\underset{\text{Orthorhombic}}{\mathop{CaS{{O}_{4}}\,\,.\,\,2{{H}_{2}}O}}\,\] \[\xrightarrow{Hardening}\underset{\begin{smallmatrix} Monoclinic \\ (Gypsum) \end{smallmatrix}}{\mathop{CaS{{O}_{4}}.\,2{{H}_{2}}O}}\,\]
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