The excess of potassium in `KCl` makes the crystal appear

Options

A. yellow
B. pink
C. violet
D. green

Answer

3

Explanation

Anion vacancies in alkali halides are produced by heating the alkali halide crystals in an atmosphere of the alkali metal vapour. When the metal atoms deposits on the surface they diffuse into the crystal and after ionization the alkali metal ion occupies cationic vacancy whereas electron occupies anionic vacancy. Electrons trapped in anion vacancies are referred to as `F` -centers (from Farbe, the German word for colour) that gives rise to interesting colour in alkali halides.
Electrons trapped in anion vacancies absorn some energy of the white light giving yellow colour to `NaCl`, pink to `LiCl` and violet to `KCl`.