Question

Frenkel defect is also known as
A) Stiochiometric defect
B) Dissociation defect
C) Impurity defect
D) Non-stoichiometric defect

Answer 1

We need to remember that a Frenkel defect is a type of point defect in crystalline solids. Frenkel defect is one in which an atom is displaced from its lattice point to the interstitial site, creating a vacancy at the lattice point. Here, since dislocation of the atom lattice point happens.

Complete answer:
We have to remember that the defect forms when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy, and becomes an interstitial by lodging in a nearby location. In elemental systems, they are primarily generated during particle irradiation, as their formation enthalpy is typically much higher than for other point defects, such as vacancies, and thus their equilibrium concentration according to the Boltzmann distribution is below the detection limit. In ionic crystals, which usually possess low coordination numbers or a considerable disparity in the sizes of the ions, this defect can be generated also spontaneously, where the smaller ion (usually the cation) is dislocated. Frenkel defects are exhibited in ionic solids with a large size difference between the anion and cation (with the cation usually smaller due to an increased effective nuclear charge)
Some examples of solids which exhibit Frenkel defects: Zinc sulphide, silver chloride.

Note:
Even though Frenkel defects involve only the migration of the ions within the crystal, the total volume and thus the density is not necessarily changed: in particular for close-packed systems, the lattice expansion due to the strains induced by the interstitial atom typically dominates over the lattice contraction due to the vacancy, leading to a decrease of density.