When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.

Explanation

The dilute solution of alkali metals in liquid ammonia exhibit dark blue colour because ammoniated electrons absorb energy corresponding the red region of the visible light .
`M + (x + y) NH_(3) to [M (NH_(3))_(x) ]^(+) + underset("Ammoniated electrons")(e^(-) (NH_(3))_(y))`
However , if the concentration increases above 3M , the colour changes to copper-bronze and the solution acquires metallic lustre due to the formationof metal ion clusters.