Q2 / 90 · JEE Main 2014 (11 Apr Online) · Chemistry

The appearance of colour in solid alkali metal halides is generally due to:

  • A
    Schottky defect
  • B
    Frenkel defect
  • C
    Interstitial position
  • Correct answer
    D
    F-centres

Solution

The appearance of colour in alkali metal halides is generally due to F-centres. F centers in $\mathrm{NaCl}$ produce a band of optical absorption towards the blue end of visible spectrum, thus the colour appears yellow under transmitted light. On the other hand, $\mathrm{KCl}$ with $\mathrm{F}$-centers appears magenta, and $\mathrm{KBr}$ appears blue.

Hence, the correct answer is option: 'D'.

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