Answer: Ammoniated electrons slowly convert to sodium amide with evolution of dihydrogen.
- A Sodium metal precipitates out unchanged
- B Ammoniated electrons slowly convert to sodium amide with evolution of dihydrogen
- C The dissolved sodium is slowly oxidised to sodium hydroxide and nitrogen gas
- D Ammonia is oxidised to nitrogen gas
Correct answer: B. Ammoniated electrons slowly convert to sodium amide with evolution of dihydrogen
Explanation: The blue colour and conductivity arise from ammoniated electrons. On standing these react: Na + NH<sub>3</sub> → NaNH<sub>2</sub> + ½H<sub>2</sub>, so the colour fades as amide forms and H<sub>2</sub> is released.
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.