Ncert Exercises & Solutions

15. Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionisation (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame?

(a) 2

(b) 13

(d) 17

(a, c)

The elements of group 1 (alkali metals) and group 2 (alkaline earth metals) have 1 and 2 electrons respectively in their valence shells and hence have low ionisation energies. In other words, elements of group 1 and 2 imparts colour to the flame.

Group 1	Colour	Group 2	Colour
Li	Crimson	Ca	Brick-red
Na	Yellow	Se	Crimson red
K	Pale violet	-	-
Rb	Red violet	Ba	Apple green
Cs	Blue	Ra	Crimson

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