Question

why do alkali or alkaline earth metal give blue color solution in liquid ammonia

Answer 1

the solvent ammonia helps to ionize the alkali metal and subsequently solvates the ion and the liberated electron. The electron is trapped by ammonia molecules.

Here x and y stands for number of ammonia molecules solvating the cation and the electron respectively and their value varies with metal to metal.

The trapped electron has higher energy levels and can be excited by ordinary visible light. In the excited state the electron again returns to ground state by emitting the energy in the form of blue light. Thus the solution appears blue.