question_answer 68)

  Schottky defect is observed in crystals when.......... (a) some cations move from their lattice site to interstitial sites (b) equal number of cations and anions are missing from the lattice (c) some lattice sites are occupied by electrons (d) some impurity is present in the lattice

Answer:

                  (b) Schottky defect is observed in crystal when equal number of cations and anions are missing from the lattice. Thus, density of solid decreases.               When some cations move. from their lattice site to interstitial site is known as Frenkel defect. When some impurity is present on crystal is known as impurity defect.                                             When lattice site is occupied by electron, this type of defect is known as metal excess defect. Hence, except (b) all statements are incorrect regarding Schottky defect.