NEET Questions Solved


What type of crystal defects is indicated in the diagram given below?

(a) Frenkel and Schottky defects
(b) Schottky defect
(c) Interstitial defect
(d) Frenkel defect

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(b) These defects are created when one +ve and one -ve ion are missing from their respective position.

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Frenkel defect is noticed in:

(a) AgBr

(b) ZnS

(c) Agl

(d) all of these

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(d) Frenkel defect is arised when the cations are missing from their lattice sites and occupy interstitial sites. As a result of Frenkel defect, density remains unchanged but dielectric constant increases.

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Choose the correct matching sequence from the possibilities given

(a) Crystal defect         (1) AB AB AB. . . . type crystal
(b) hcp                        (2) Covalent crystal
(c) CsCl                      (3) Frenkel
(d) Diamond               (4) Face centered in cube
(e) NaCl                     (5) Body centered in cube
     
     (a) (b) (c) (d) (e)

(A)  3   1   2    5    4

(B) 3    1   5   2     4

(C) 3    5   1   2     4

(D) 5    3  4   2      1

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(B). Crystal defects are referred as Frenkel and Schottsky defects.

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Frenkel defect is not found in the halides of alkali metals because alkali metals have

1. high electropositivity
2. high ionic radii
3. high reactivity
4. ability to occupy interstitial sites

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(2) 

Frenkel defect is not found in pure alkali metal halides. This is because of the larger size of the cations of the alkali metals, due to the large size the cations cannot fit into the interstitial sites.

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Schottky defect occurs mainly in electrovalent compound where 

1. Positive ions have large sizes

2. Negative ions have small sizes

3. Positive and negative ions are of similar size

4. Positive ions are big and negative ions are small

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(3) Schottky defect occurs mainly in electrovalent compound where positive and negative ions are of similar size.

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The appearance of colour in solid alkali metal halides is generally due to :-

1. Frankel Defect
2. Interstitial Defect
3. F-Centres
4. Schottky Defect

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(3) The appearance of colour in solid alkali metal halides is generally due to F-centres.

 

 

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NEET - 2017

Which is the incorrect statement?

(a) FeO0.98 has non-stoichiometric metal excess defect

(b) Density decreases in case of crystals with Schottky's defect

(c) NaCI(s) is insulator, silicon is semiconductor, silver is conductor, quartz is piezoelectric crystal

(d) Frenkel defect is favoured in those ionic compounds in which sizes of cation and anions are almost equal

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

(a)  FeO0.98 has non-stoichiometric metal excess defect. 

(b) In an ionic crystal of A+B- type, if equal number of cations and anions are missing from their lattice sites, the defect is called Schottky defect. Due to such defect, density of solid decreases. Thus, statement (b) is correct.

(c) NaCl-insulator Silicon (Si) -semiconductor. Silver (Ag) - conductor; Quartz - piezoelectric crystal.

Thus, statement (c) is correct.

(d) In an ionic crystal when an j£n is missing from its lattice site and occupies interstitial site, the defect is called Frenkel defect. This type of defect is seen in those crystals where the difference in the size of cations and anions is very large and their coordination number is low. Thus, statement (d) is incorrect.

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NEET - 2015

The correct statement regarding defects in the crystalline solid is

(a) Schottky defects have no effect on the density of crystalline solids

(b) Frenkel defects decreases the density of crystalline solids

(c) Frenkel defcct is a dislocation defect

(d) Frenkel defect is found in halides of alkaline metals

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

In Frenkel defect, ions in solids dislocate from their positions. Hence, Frenkel delect is a dislocation defect.

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NEET - 2006

The appearance of colour; in solid alkali metal halides is generally due to:-

(a) F-centres
(b) Schottky defect
(c) Frenkel defect
(d) interstitial positions

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

The appearance of colour in solid alkali metal halides is generally due to F-centres.

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BOARD

Analysis shows that FeO has a non-stoichiometric composition with formula Fe0.95O. Give reason.

                                                                                                              1mark

Concept Videos :-

#31 | Crystal Defects: Frenkel Defect
#32 | Crystal Defects: Metal Excess Defect
#33 | Crystal Defects: Metal Deficiency Defect

Concept Questions :-

Imperfections in Solids

Show metal deficiency defect / It is a mixture of Fe2+ and Fe3+Fe2+ions are replaced by Fe3+/Some of the ferrous ions get oxidised to ferric ions.                                                         1mark 

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