Answer: NaOH.
- A NaOH
- B Na<sub>2</sub>CO<sub>3</sub>
- C NaHCO<sub>3</sub>
- D NaCl
Correct answer: A. NaOH
Explanation: Sodium hydroxide (NaOH) is commonly called caustic soda; it is a strong base used in soap making.
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.