Question

expalin why the solution of alkali metal in liquid ammonia is blue in colour

Answer 1

The solution of alkali metals in ammonia contains ammoniated cations and ammoniated electrons as follows:

M + ( x+ y)NH₃ --> M⁺ (NH₃)_x + e^- (NH₃)_y

now, when an ordinary light falls over these ammoniated electrons, they get excited to higher levels by absorbing energy corresponding to red region of visible light.

As a result the transmitted light from the solution is blue which imparts blue color to the solution of alkali in liq. ammonia.