Question

Nacl appers yellow in colour on heating why?

Answer 1

This is because of the presence of chlorine .On heating chlorine, it turn yellow colour. When NaCl is heated ,the same criteria takes place

Answer 2

This yellow colour is due to metal excess defect of anionic valency.

Na+ion deposited on the surface of crystal of NaCl . The Cl-ion diffused to form NaCl. This happens by loss of electron from Na to Na+.

The released electro diffused into the crystal and occupy anionic site called F center which imparts yellow colour to NaCl.