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JEE Main levelOne or more correct optionsDifficulty 2 of 3ss193

Which of the following statements about point defects are correct?

  1. ASchottky defects decrease the density of the crystal.
  2. BSchottky defects are favoured when the cation and anion are of very different size and the coordination number is low.
  3. CA Frenkel defect creates a vacancy and an interstitial of the same ion.
  4. DHeating in potassium vapour gives F-centres and the crystal becomes violet.

Answer: A, C, D

Schottky defects remove ions, lowering density (true). A Frenkel defect is a vacancy plus an interstitial of the displaced ion (true). Schottky defects are favoured when ions are of similar size and CN is high; very different sizes with low CN favour Frenkel (false). KCl heated in K vapour acquires anion vacancies with trapped electrons, F-centres, giving a violet colour (true).
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