Copper and chlorine compounds makes blue fire work. Why?

Explanation

To produce colours, fire works experts burn the metal and chlorine together in a vapour, where the two elements are gases instead of solid.
(ii) The burning excites the electron pushing them into a higher than normal the electrons returns to their normal level, they release their extra energy as a colour burst of light.
(iii) True blue fireworks are the hardest to make since the compound copper breaks down in a hot flame