When a metal of group $1$ was dissolved in liquid ammonia,the following observations were obtained :
$(a)$ Blue solution was obtained initially.
$(b)$ On concentrating the solution,the blue colour changed to bronze colour.
How do you account for the blue colour of the solution? Give the name of the product formed on keeping the solution for some time.

(N/A) Alkali metals dissolve in liquid ammonia to form a blue solution due to the presence of ammoniated electrons. These electrons absorb energy in the visible region of light and impart a blue colour to the solution.
$M + (x+y) NH_{3} \rightarrow [M(NH_{3})_{x}]^{+} + [e(NH_{3})_{y}]^{-}$
$(b)$ In a concentrated solution,the blue colour changes to bronze colour due to the formation of metal ion clusters. On standing,the blue solution liberates $H_{2}$ gas and forms a metal amide.
$M^{+} + e^{-} + NH_{3} \rightarrow MNH_{2} + \frac{1}{2} H_{2}$
The product formed is a metal amide.