Answer: 13.
- A 13
- B 1
- C 7
- D 10
Correct answer: A. 13
Explanation: NaOH is a strong base. [OH-] = 0.1 M, pOH = 1, pH = 14 - 1 = 13.
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.