Question

F-centres are

• A. the neutrons trapped in anionic vacancies.
• B. the electrons trapped in anionic vacancies.
• C. the electrons trapped in cation vacancies.
• D. non equivalent sites of stoichiometric compounds.

Answer 1

The correct option is B

the electrons trapped in anionic vacancies.

The anionic sites occupied by unpaired electrons are called F-centres (from the German word Farbenzenter for colour centre). Such defects also impart color to the crystals. The color results by excitation of these electrons when they absorb energy from the visible light falling on the crystals. For example, impart yellow color to the crystals of NaCl.