Question

Alkali metals impart colour to bunsen flame due to

Answer 1

Alkali metals impart characteristic colours to the flame due to low ionisation enthalpy

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Answer 2

hey mate , here's your answer.....

The energy of the ''Bunsen Flame'' is sufficient to excite the electrons of the ''Alkali Metals"to higher energy level.
Therefore , the electrons emit energy and come back to the original levels. This emitted energy falls in the visible region of electromagnetic spectrum. This is why, alkali metals impart colour to flame.

....hope this helps....