The Solid State

Question 209
CBSEENCH12005557

What makes the crystal of KCl appear sometimes violet?

Solution
This is due to F centre, electron become exicted and when they come to ground state they radiate energy in visible reigon.
Question 210
CBSEENCH12005558

What is the effect of Schottky and Frenkel defects on the density of crystalline solids?

Solution

Schottky defect decrease the density solid where as no such defect arise due to frenkel defect.

Question 211
CBSEENCH12005559

What is the maximum possible coordination number of an atom in an hcp crystal structure of an element?

Solution

The maximum possible coordination number of an atom in hcp structure of an element is 12.

Question 212
CBSEENCH12005560

How many atoms can be assigned to its unit cell if an element forms
(i) a body centred cubic cell, and (ii) a face centred cu
bic cell?

Solution

Body centre wholly belongs to the unit cell in which it is present. Thus
in a body-centered cubic (bcc) unit cell:
(i) 8 corners × 1/8per corner atom= 8 x 1/8 = 1 atom
(ii) 1 body centre atom = 1 × 1 = 1 atom
∴ Total number of atoms per unit cell = 2 atoms
For face centred 

(i) 8 corners atoms × 1/8 atom per unit cell
= 8  x1/8 = 1 atom

(ii) 6 face-centred atoms ×1/2 atom per unit cell = 6 ×1/2 = 3 atoms
∴ Total number of atoms per unit cell = 4 atoms

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