Q. The appearance of colour in solid alkali metal halides is generally due to :
A) F-centres
B) Schottky defect
C) Frenkel defect
D) Interstitial positions
Explanation
[Solution from source] When alkali halide crystals are heated in alkali-metal vapour, anion vacancies form and trap electrons; these F-centres absorb visible light and colour the crystal (e.g. NaCl turns yellow). Schottky and Frenkel defects by themselves do not produce colour. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.