22
MCQ (Single Correct Answer)
Which of the following point defects are shown by $\mathrm{AgBr}(\mathrm{s})$ crystals?
1. Schottky defect
2. Frenkel defect
3. Metal excess defect
4. Metal deficiency defect
A
1 and 2
B
3 and 4
C
1 and 3
D
2 and 4
23
MCQ (Single Correct Answer)
In which pair most efficient packing is present?
A
hcp and bcc
B
hcp and ccp
C
bcc and ccp
D
bcc and simple cubic cell
24
MCQ (Single Correct Answer)
The percentage of empty space in a body centred cubic arrangement is ........... .
A
74
B
68
C
32
D
26
25
MCQ (Single Correct Answer)
Which of the following statement is not true about the hexagonal close packing?
A
The coordination number is 12
B
It has $74 \%$ packing efficiency
C
Tetrahedral voids of the second layer are covered by the spheres of the third layer
D
In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer
26
MCQ (Single Correct Answer)
In which of the following structures coordination number for cations and anions in the packed structure will be same?
A
$\mathrm{Cl}^{-}$ions form fcc lattice and $\mathrm{Na}^{+}$ions occupy all octahedral voids of the unit cell
B
$\mathrm{Ca}^{2+}$ ions form fcc lattice and $\mathrm{F}^{-}$ions occupy all the eight tetrahedral voids of the unit cell
C
$\mathrm{O}^{2-}$ ions form fcc lattice and $\mathrm{Na}^{+}$ions occupy all the eight tetrahedral voids of the unit cell
D
$\mathrm{S}^{2-}$ ions form fcc lattice and $\mathrm{Zn}^{2+}$ ions go into alternate tetrahedral voids of the unit cell