The correct statement about the Frenkel defect (FD) is

• A

  FD decreases the density of the substance.
• Correct answer
  B

  FD occurs due to the dislocation of some of the smaller ions from their original positions to the interstitial sites.
• C

  FD is a vacancy defect that results due to missing of an equal number of cations and anions, from a crystal lattice.
• D

  FD is found in all ionic solids.

Hence, the correct answer is option: 'B'.