Answer: Solvated electrons (e-(am)) absorbing light in the visible range.
- A Solvated electrons (e-(am)) absorbing light in the visible range
- B Sodium cations themselves absorbing visible light in solution
- C Liquid ammonia itself possessing an inherent blue colour
- D Trace amounts of dissolved sodium oxide colouring the solution
Correct answer: A. Solvated electrons (e-(am)) absorbing light in the visible range
Explanation: Solvated electrons (free electrons surrounded by NH<sub>3</sub> molecules) absorb light broadly; dilute solutions are blue, concentrated solutions are metallic bronze.
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.