1

### AIPMT 2007

The fraction of total volume occupied by the atoms present in a simple cube is
A
${\pi \over {3\sqrt 2 }}$
B
${\pi \over {4\sqrt 2 }}$
C
${\pi \over 4}$
D
${\pi \over 6}$

## Explanation

The maximum properties of the available volume which may be filled by hard sphere in simple cubic arrangement is ${\pi \over 6}$ or 0.52.
2

### AIPMT 2006

CsBr crystallises in a body centered cubic lattice. The unit cell length is 436.6 pm. Given that the atomic mass of Cs = 133 and that of Br = 80 amu and Avogadro number being 6.02 $\times$ 1023 mol$-$1, the density of CsBr is
A
4.25 g/cm3
B
42.5 g/cm3
C
0.425 g/cm3
D
8.25 g/cm3

## Explanation

Density of CsBr = ${{Z \times M} \over {V \times {N_A}}}$

= ${{1 \times 213} \over {{{\left( {436.6 \times {{10}^{ - 10}}} \right)}^3} \times 6.023 \times {{10}^{23}}}}$

= 4.25 g/cm3
3

### AIPMT 2006

The appearance of colour in solid alkali metal halides is generally due to
A
interstitial positions
B
F.-centres
C
Schottky defect
D
Frenkel defect

## Explanation

F-centres are the sites where anions are missing and instead electrons are present. They are responsible for colours.
4

### AIPMT 2005

In a face-centered cubic lattice, a unit cell is shared equally by how many unit cells?
A
2
B
4
C
6
D
8

## Explanation

In given unit cell it is shared equally by six faces of different unit cells.