Question:medium

When crystals of sodium chloride are heated in the presence of sodium vapour, they turn yellow. This is due to the formation of:

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Excess metal defect: an electron trapped in an anion vacancy produces colour.
Updated On: Jul 3, 2026
  • Schottky defects
  • Frenkel defects
  • F-centres
  • H-centres
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The Correct Option is C

Solution and Explanation

Schottky and Frenkel defects don't inherently produce colour. This is a metal excess defect (anion vacancy + trapped electron), which absorbs visible light causing yellow colour.
\[\boxed{\text{F-centres}}\]
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