PCI5 molecule has

(1) three fold axis of symmetry

(2) two fold axis of symmetry

(3) both

(4) none of these

Concept Questions :-

Introduction and Type of Crystal System
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Which of the following statements is correct about the conduction of electricity in pure crystal of silicon atroom temperature?

(1) The conduction is due to electrons present in fully occupied lowest energy states.

(2) The conduction is due to only some electrons capable of leaving the bonds at room temperature.

(3) The conduction is only due to the holes formed from the release of electrons.

(4) The conduction is due to the movement of both the electrons released and holes formed.

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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Calculate the Miller indices of crystal planes which cut through the crystal axes at (i) (2a, 3b, c), (ii) (∞, 2b, c )

(1) 3, 2, 6 and 0, 1, 2

(2) 4, 2, 6 and 0, 2, 1

(3) 6, 2, 3 and 0, 0, 1

(4) 7, 2, 3 and 1, 1, 1

Concept Questions :-

Introduction and Type of Crystal System
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Caculate the distance between 111 planes in a crystal of Ca. Repeat the calculation for the 222 planes. (a = 0.556nm)

(1) 016.1 nm

(2) 0.161 nm

(3) 0.610 nm

(4) None of the above

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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A metallic element crystallizes into a lattice containing a sequence of layers of ABABAB ............ Any packing of spheres leaves out voids in the lattice. The percentage by volume of empty space of this is

(1) 26%

(2) 21%

(3) 18%

(4) 16 %

Concept Questions :-

Introduction and Type of Crystal System
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Silver metal crystallises in a cubic closest – packed arrangement with the edge of the unit cell having a length a = 407 pm. What is the radius of silver atom.

(1) 143.9 pm

(2) 15.6 pm

(3) 11.59 pm

(4) 13.61 pm

Concept Questions :-

Introduction and Type of Crystal System
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From the fact that the length of the side of a unit cell of lithium is 351 pm. Calculate its atomic radius. Lithium forms body centred cubic crystals.

(1) 152.69 pm

(2) 62.71 pm

(3) 151.98 pm

(4) 54.61 pm

Concept Questions :-

Introduction and Type of Crystal System
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Atomic radius of silver is 144.5 pm. The unit cell of silver is a face centred cube. Calculate the density of silver.

(1) 10.50 g/cm3

(2) 16.50 g/cm3

(3) 12.30 g/cm3

(4) 15.50 g/cm3

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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Lithium borohydride (LiBH4),crystallises in an orthorhombic system with 4 molecules per unit cell. The unit cell dimensions are : a = 6.81Å, b= 4.43Å, c=7.17Å. If the molar mass of LiBH4 is 21.76 g mol–1. The density of the crystal is –

(1) 0.668 g cm–3

(2) 0.585 g cm2

(3) 1.23 g cm–3

(4) None

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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A metallic elements exists as a cubic lattice. Each edge of the unit cell is 2.88Å. The density of the metal is 7.20 g cm–3. How many unit cells will be present in 100 gm of the metal.

(1) 5.82 × 1023

(2) 6.33 × 1023

(3) 7.49 × 1024

(4) 6.9 × 1024

Concept Questions :-

Density/Formula/packing fraction/ Semiconductors
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