Answer: Ca(OH)2.
- A Ca(OH)2
- B CaO
- C CaCO3
- D CaSO4
Correct answer: A. Ca(OH)2
Explanation: Slaked lime Ca(OH)2 is produced when water is added to quicklime: CaO + H2O → Ca(OH)2.
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.