Frenkel defect is vacancy as well as interstitial defect as atom leaves its place in lattice creating a vacancy and occupy interstitial site in a nearby location. Hence, statement I is true. Frenkel defect does not leads to colour in ionic solids due to absence of F - centres. lonic solids having anionic vacancies because of metal excess defects. This leads to colour in ionic solids due to presence of F - centres. Hence, statement II is false.