Question

Sodium chloride crystals are heated.​

Answer 1

Answer:

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.

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Answer 2

Answer:

On heating sodium chloride with sodium vapors, the chloride ions diffuse to the surface of the crystals and combine with Na atoms which get ionized to Na+ ions by loosing electrons. These electrons get trapped in anion vacancies and act as F − centres which impact yellow colour to the atom.