Answer: CaSO4·2H2O.
- A CaSO4·2H2O
- B CaSO4·0.5H2O
- C CaCO3
- D Ca(OH)2
Correct answer: A. CaSO4·2H2O
Explanation: Gypsum is calcium sulfate dihydrate (CaSO4·2H2O), a naturally occurring mineral.
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.