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The Solid State — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe Solid State3 Marks
Question
Why does table salt, $NaCl,$ some times appear yellow in colour?
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Answer

Yellow colour in sodium chloride is due to metal excess defect. Iin metal excess defect anionic vacancies are created due to diffusion of $Cl^-$ to the surface of the crystal and there after unpaired electrons occupy anionic sites. These sites are called $F-$centres. The electrons at $F-$cetres then absorb energy from the visible region for the excitation which makes crystal appear yellow.

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