When metallic sodium is dissolved in liquid ammonia, the resulting blue solution is due to the presence of which species?

Solution

1. Alkali metals dissolve in liquid ammonia to form a blue solution.
2. The dissolution process is represented as $\text{M}+(x+y){\text{NH}}_3\to [\text{M}({\text{NH}}_3{)}_x{]}^{+}+[e({\text{NH}}_3{)}_y{]}^{-}$.
3. The blue color is specifically due to the absorption of light by the ammoniated electrons, which promotes them to higher energy levels.
4. Hence the answer is (B).