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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