When sodium metal is dissolved in liquid ammonia, blue colour solution is formed. The blue colour is due to

When sodium metal is dissolved in liquid ammonia to form colored solution. Dilute solutions are bright blue in colour due to the presence of solvated electrons.

$\mathrm{Na} + \left(\mathrm{x} + \mathrm{y}\right){\mathrm{NH}}_3 \to {\left[\mathrm{Na}{\left({\mathrm{NH}}_3\right)}_{\mathrm{x}}\right]}^{+} + {\left[\mathrm{e}\left({\mathrm{NH}}_3\right)\right]}^{-}$

                                                                   Blue Colour