Explain the following terms with subitable examples :
`{:((i),"Frenkel defect",(ii),"F-centres"):}`

Explanation

(i) Frenkel defect : If an ion is missing from its lattice site and occupies the interstitial site, to make it electrically and stoichiometrically natural. This type of defect is called frenkel defect.
(ii) F-centres: The site where electron is entrapped in the anion vacancy is called F-centres.