What makes alkali metal halides sometimes coloured, which are oth

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 Multiple Choice QuestionsShort Answer Type

81. Name a salt that can be added to AgCl so as to produce cation vacancies.
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 Multiple Choice QuestionsLong Answer Type

82.

How many lattice points are there in one unit cell of each of the following lattice?
(a) face centred cubic
(b) face centred tetragonal
(c) body centred cubic

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 Multiple Choice QuestionsShort Answer Type

83. Find out the number of atoms per unit cell in a face-centred cubic structure having only single atoms at its lattice points.
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84. What makes alkali metal halides sometimes coloured, which are otherwise colourless?


Metal excess defect is resposible for colour in alkylhalides.

When crystals of NaCl are heated in an atmosphere of sodium vapour, the sodium atoms are deposited on the surface of the crystal.
The Cl– ions diffuse to the surface of the crystal and combine with Na atoms to give NaCl. This happens by loss of electron by sodium atoms to form Na+ ions. The released electrons diffuse into the crystal and occupy anionic sites and impart colour.

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85. What is the difference between ccp and fcc lattice?
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86. What percent of space is utilised by spheres in (i) simple cubic, (ii) face-centered cubic, (iii) body-centered cubic structure?
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87. If three elements A, B and C crystallize in a cubic solid lattic with A atom at the corner, B atoms at cube centre and C atoms at edges then what would be the formula of the solid?
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88. Out of Schottky and Frenkel defect which increases the dielectric constant of crystals?
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89. What are extrinsic semi-conductor?
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90. What is Photovoltaic.
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