This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Setting of POP is the result of: \nSelect and explain. \nA. Difference in solubility of CaSO4.1/2 H2O + CaSO4. 2H2O, B. Reaction between CaSO4. 2H2O and water, C. Nucleation and growth of CaSO4.1/2 H2O crystals, D. Reaction between hemihydrate and dihydrate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: SETTING REACTIONS\nThe most widely accepted mechanism is the dissolution-precipitation theory, which is based on dissolution of the hemihydrate particles in water followed by instant recrystallization to the dihydrate. This reaction has become possible because the solubility of hemihydrate in water is four times greater than that of the dihydrate near room temperature. Thus, the setting reactions occur as follows:\n\nWhen the hemihydrate is mixed with water, a suspension is formed that is fluid and workable.\nThe hemihydrate dissolves until it forms a saturated solution of Ca2+\xa0 and (SO4)2−.\nThis saturated hemihydrate solution is supersaturated with respect to the solubility of the dihydrate; precipitation of dihydrate occurs.\n\nKey Concept:\nSetting reaction has become possible because the solubility of hemihydrate in water is four times greater than that of the dihydrate near room temperature.\nReference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 183', 'role': 'assistant'}]