Question

why does
different alkali metals impart different colours?
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Answer 1

Explanation:

the electrons emit energy and come back to the original levels. this emitted energy falls in the visible. the region of the electromagnetic spectrum. this is why alkali metals impart colours to flame.

Answer 2

Question:-

Why does different alkali metals impart different colours?

Answer:-

Alkali metals have very low value of ionisation energy as compared to other metals.

So, alkali metals easily get excited and impart colour to flame.