A body centred cubic arrangement is shown : O is the body centre; A, B, C, D,......., H are the corners. What is the magnitude of the angle AOB ?

(A) 120°                                 

(B) 109°28'

(C) 104°31'                           

 (D) 70°32'

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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A rhombohedral unit cell is shown. What is its volume ?
Side length = a Å.

(A) a33                               

(B) a332

(C) a32                             

(D) a3 32

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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A crystal formula AB3 has A ions at the cube corners and B ions at the edge centres. The coordination numbers of A and B are respectively 

(A) 6 and 6                                                 

 (B) 2 and 6

(C) 6 and 2                                                 

 (D) 8 and 8

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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A metal crystallizes in two cubic phases, face centred cubic (fcc) and body centred cubic (bcc) whose unit cell length are 3.5 and 3.0 Å respectively. Calculate the ratio of density of fcc and bcc. 

(A) 2.123                                     

 (B) 1.259

(C) 5.124                                       

(D) 3.134

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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Assertion :  The stability of a crystal gets reflected in its melting point.

Reason :  The stability of a crystal depends upon the strength of the interparticle attractive force. The melting point of a solid depends on the strength of the attractive force acting between the constitutent particles.

  1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
  2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
  3. If the assertion is true but the reason is false
  4. If both the assertion and reason are false

Concept Questions :-

Introduction and Type of Crystal System
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Assertion :  The melting point decreases in the order.
Water > ethyl alcohol > diethylether > methane

Reason : The strength of the intermolecular forces between these molecules follow the order
Water > ethyl alcohol > diethylether > methane

  1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
  2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
  3. If the assertion is true but the reason is false
  4. If both the assertion and reason are false

Concept Questions :-

Introduction and Type of Crystal System
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In a face centred cubic arrangement of metallic atoms, what is the relative ratio of the sizes of tetrahedral and octahedral voids ?

(A) 0.543                                   

 (B) 0.732

(C) 0.414                                   

(D) 0.637

Concept Questions :-

Voids and radius ratio/coordination number
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Close packing is maximum in the crystal which is-

(A) Simple cube                               

(B) bcc

(C) fcc                                             

(D) None

Concept Questions :-

Voids and radius ratio/coordination number
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The rank of a cubic unit cell is 4. The type of cell as-

(A) Body centred                               

(B) Face centred

(C) Primitive                                     

(D) None of these

Concept Questions :-

Introduction and Type of Crystal System
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Bragg’s equation is-

(A) nλ=2θsinθ                               

(B) nλ=2dsinθ

(C) 2nλ=dsinθ                               

(D) λ=2d/nsinθ

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