What are f-centers ?

1.	What are f-centers ?
Answer» `to` f-centers are the anionic sites occupied by unpaired electrons . `to` These impart colour to cyrstals . This colour is due to the excitation of electrons when they absorb energy from the visible light . `to` f- centres are formed by heating alkyl halide with excess of alkali metal . E.g : NaCl crystal heated in presence of Na-vapour yellow colour is produced due to f-centres .

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