1. THE SOLID STATE TEST 2

Schottky defect is observed in crystals when

• some cations move from their lattice site to interstitial sites

• equal number of cations and anions are missing from the lattice

• some lattice sites are occupied by electrons

• some imurity is present in the lattice

Frenkel defect is observed in crystals when

• some cations move from their lattice site to interstitial sites

• equal number of cations and anions are missing from the lattice

• some lattice sites are occupied by electrons

• some imurity is present in the lattice

Which statement is true about Schottky Defect?

• It is observed in compounds having low coordination number

• It is usually favoured by a very small difference in the sizes of cation and anion

• It increases the density of the crystal lattice

• It is a non-stoichiometric point defect

Which statement is not true about Frenkel Defect?

• It is observed in compounds having low coordination number

• It is usually favoured by a large difference in the sizes of cation and anion

• It decreases the density of the crystal lattice.

• It is a stoichiometric point defect observed in ionic solids.

The coordination number in NaCl (fcc), ZnS (ccp) and CsCl (bcc) is 6, 4 and 8 respectively. The ionic compounds which will be exhibiting Schottky Defect will be

• NaCl, ZnS

• ZnS, CsCl

• NaCl, CsCl

• all will exhibit

The only silver halide which can exhibits Schottky as well as Frenkel defect is

• AgF

• AgCl

• AgBr

• AgI

In METAL EXCESS DEFECTS the sites where an electron gets trapped in the anionic vacancy disturbing the ratio of cation to anion is known as

• E- CENTRE

• F- CENTRE

• G- CENTRE

• I- CENTRE

KCl when heated in an atmosphere of Potassium vapours exhibit purple colour. This arises due to which type of defect?

• metal excess defect due to anionic vacancies.

• metal excess defect due to presence of extra cation.

• metal deficient defect due to variable oxidation state of metal.

• impurity defect when a foreign ion is present in the crystal lattice.

The metal deficiency defect which occurs when the metal can exhibit variable valencies is usually observed in oxides of

• alkali metals

• alkaline earth metals

• transition metals

• all of the above

When NaCl crystal is doped with MgCl ₂ , the nature of defect produced is

• Schottky defect

• Frenkel defect

• Impurity defect

• none of the above