Reaction of alkali metals in liquid ammonia are blue in colour because
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Solvated electron. ... The solvated electron is responsible for a great deal of radiation chemistry. Alkali metals dissolve in liquid ammonia giving deep blue solutions which are conducting in nature. The blue colour of the solution is due to ammoniated electrons which absorb energy in the visible region of light.
The alkali metals like Na,K etc. dissolved in liquid Ammonia giving deep blue coloured solution.This solution is highly conducting in nature.It contains a large amount of Ammoniated captions as well as electrons as shown below in the reaction:-M + ( a + b )NH3 => M* ( NH3 )a + e(NH3)bIt has been found that the blue colour of solution is mainly due to the presence of the Ammoniated electrons in the solution.These electrons absorb energy corresponding to the red region of the visible light spectrum for its excitation to the higher energy levels.The transmitted light is blue coloured, thus it imparts blue colour to the solution.The solution is paramagnetic due to the presence and in the absence of catalysts and impurities decomposes the blue coloured solution and it gives formation to "Metal amide" and liberation of hydrogen gas.