Question

Why are crystals having F-centres paramagnetic?

Answer 1

1. An F-centre (short for Farbe centre, meaning “colour centre”) forms when an anion (like Cl⁻) is missing from its lattice site, and the vacancy is occupied by an unpaired electron.
2. These unpaired electrons are free to align with an external magnetic field.
3. Since paramagnetism arises due to unpaired electrons, crystals with F-centres exhibit paramagnetic behaviour.