Question

In the following figure, the blank $X$ is known as _______ and why?

• A. Electron trap, because an electron is present here
• B. Metal deficient centre, since negative charge is present here
• C. $F$-centre, since it imparts colour to the crystal
• D. $F$-centre, since it is responsible for positive charge on the crystal

Answer 1

Answer: (C)

The anionic sites occupied by the unpaired electrons are called $F$-centres from the German word Farbenzenter for colour centre.