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NEET levelSingle correct optionDifficulty 1 of 3ss094

The colour of NaCl heated in sodium vapour is due to

  1. AFrenkel defects
  2. BSchottky defects
  3. CF-centres: electrons trapped in anion vacancies
  4. DCation vacancies filled by Na

Answer: C

Excess Na atoms deposit on the surface and ionise. The released electrons diffuse into anion vacancies (F-centres) and absorb visible light, giving the yellow colour.
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