Question

Give reason a crystal of nacl shows yellow colour on heating in sodium vapour

Answer 1

the yellow color acquired by the NaCl crystal is due to defect called metal excess defect due to anionic vacancy.
When crystals of NaCl is heated in an atmosphere of sodium vapor the sodium ion are deposited on the surface of crystal. The Cl- ion diffuse to form NaCl. This happens by loss of electron by Na to form Na+.The released electron diffuse into the crystal and occupy anionic site. These are called F centre and it imparts yellow color to NaCl

Answer 2

Explanation:

Sodium chloride on heating with sodium vapours acquires yellow colour because sodium chloride crystal suffers metal excess defect with sodium vapours on heated condition. Due to electronic transition at the excited state of sodium atom, it appears yellow.