An excess of potassium ions makes KCl crystals appear violet or lilac in colour since ________.
An excess of potassium ions makes KCl crystals appear violet or lilac in colour since ________.

(i) some of the anionic sites are occupied by an unpaired electron.

(ii) some of the anionic sites are occupied by a pair of electrons.

(iii) there are vacancies at some anionic sites.

(iv) F-centres are created which impart colour to the crystals.

 

 

Correct Answers:

(i) some of the anionic sites are occupied by an unpaired electron.

(iv) F-centres are created which impart colour to the crystals.

Explanation: When KC1 is burned by K vapor, some chlorine ions leave their lattice space and form anion gaps. This chloride ion seeks to combine with K vapor to form potassium chloride. In this way the K atom loses its electron form K ions. This released electron disperses into a crystal to get stuck in an anion space called the F-center. When visible light falls on a crystal, this trapped electron gains energy, going to a higher level when it returns to earth, the energy being released in the form of light.