Answer: CaO.
- A CaO
- B Ca(OH)<sub>2</sub>
- C CaCO<sub>3</sub>
- D CaSO<sub>4</sub>
Correct answer: A. CaO
Explanation: Quicklime (CaO) is produced by heating limestone: CaCO<sub>3</sub> → CaO + CO<sub>2</sub> (calcination).
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.