Option (1): Frenkel defect occurs in compounds in which (i) coordination number is low (ii) anions are much larger in size than cations. Option (2): Frenkel defect arises when an ion is dislocated from its normal position causing a vacancy or a hole and occupied an interstitial site between the lattice points. Option (3): The electrons trapped in anion vacancies are referred as F-centers so trapping of electrons takes place and not protons. Option (4): Because of presence of large no. of vacancies in crystals in Schottky defects its density is markedly lowered.