. Alkali metals give colouration when heated in Bunsen flame. Give reason.

Explanation

When the alkali metals salts moistened with concentrated hydrochloric acid are near a platinum wire in a flame, they show characteristic coloured flame
Lithium        Crimson red
Sodium   Yellow
Potassium    Lilac
Rubidium   Reddish violet
Caesium     Blue
The heat in the flame excites the valence electron to a higher energy level. W back to its actual energy level, the excess ne excess energy is emitted as light whose wa in the visible region produces colour.