Answer: Ca(OH) 2.
- A Ca(OH)<sub>2</sub>
- B CaO
- C CaCO<sub>3</sub>
- D CaSO<sub>4</sub>
Correct answer: A. Ca(OH)<sub>2</sub>
Explanation: Slaked lime Ca(OH)<sub>2</sub> is produced when water is added to quicklime: CaO + H<sub>2</sub>O → Ca(OH)<sub>2</sub>.
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.