Answer: Rehydration: CaSO4·0.5H2O + 1.5H2O → CaSO4·2H2O (gypsum).
- A Rehydration: CaSO4·0.5H2O + 1.5H2O → CaSO4·2H2O (gypsum)
- B Dehydration of the hemihydrate to anhydrous calcium sulfate
- C Oxidation of the sulfate ion to a higher oxidation state
- D Reduction of calcium sulfate to elemental calcium and sulfur
Correct answer: A. Rehydration: CaSO4·0.5H2O + 1.5H2O → CaSO4·2H2O (gypsum)
Explanation: Plaster of Paris absorbs water to rehydrate back to gypsum, forming an interlocked crystalline structure that is hard.
Each s-block metal ion emits a characteristic flame colour because heating excites electrons to higher energy levels; light is emitted as they fall back, with the colour determined by the specific energy gap.
Concept context
Group 1 (alkali metals) and Group 2 (alkaline earth metals). Learn their reactions with water and air, important compounds like NaOH, Na₂CO₃, and CaCO₃, and anomalous behaviour of lithium and beryllium.