1. Number of particles in a primitive cubic unit cell is:
a) 1
b) 2
c) 3
d) 4
Explanation: In a primitive cubic cell, 8 atoms are present at the eight vertices of the cube. However, each atom is shared by eight unit cells. Hence, only one-eighth of each of the eight atoms is present in one primitive cubic cell.
2. In which of the following Bravais lattices none of the sides are equal?
a) Triclinic
b) Monoclinic
c) Orthorhombic
d) All of the mentioned
Explanation: Each of the above mentioned lattices have all axial distances unequal. Moreover, triclinic, monoclinic, and orthorhombic lattices have none, two and all axial angles as right angles respectively.
3. Graphite is a common allotrope of Carbon. Its crystal structure is:
a) Cubic
b) Monoclinic
c) Orthorhombic
d) Hexagonal
Explanation: Graphite crystals consist of several planar layers of Carbon atoms arranged in interconnected hexagonal rings. Each atom makes three &sigma bonds and one &pi bond. VSEPR theory predicts a trigonal planar molecular structure with respect to each Carbon atom.
4. Which of the following lattices has the highest void fraction?
a) Hexagonal close packed
b) Body centered cubic
c) Face centered cubic
d) Primitive cubic
Explanation: Void fraction = 1 − packing efficiency
Since primitive cubic unit cell has least packing efficiency out of those mentioned above, hence it has the highest void fraction of (1 − 0.52 = ) 0.48 or 48 %
5. Which of the following unit cells do not exist for tetragonal lattices?
a) Primitive centered unit cell
b) Body centered unit cell
c) Face centered unit cell
d) All of the mentioned exist
Explanation: Tetragonal lattices exist only in primitive and body centered unit cells. Face centered unit cells occur only for cubic and orthorhombic lattices.
6. Most unsymmetrical Bravais lattice in terms of axial distances and angles is:
a) Monoclinic
b) Triclinic
c) Rhombohedral
d) Hexagonal
Explanation: For triclinic lattice, none of the adjacent sides are equal in length; neither are any axial angles equal. Hydrated copper (II) sulphate and boric acid have triclinic crystals.
7. Coordination number of HCP and FCC lattices respectively are:
a) 12, 12
b) 4, 4
c) 12, 8
d) 8, 8
Explanation: Coordination number is the number of atoms that are in direct contact of any particular atom or it is the number of nearest neighbours.
8. Number of particles in one unit cell of HCP lattice is:
a) 1
b) 2
c) 4
d) 6
Explanation: Consider the top and bottom layers. One-sixth of each of the 12(=6×2) atoms located at the vertices of the two hexagons belong to the cell. Also half of the atoms at the centre of each of the two hexagons are also part of the cell. Three more atoms are present between two hexagonal planes.
9. Standard axial ratio for metallic HCP lattice is 2√( 2/3). It is the ratio of
a) Atomic radius to hexagon edge length
b) Hexagon height length to atomic radius
c) Atomic radius to hexagon height
d) None of the mentioned
Explanation: Ratio of the height of the hexagonal unit cell to its edge length is called the axial ratio, usually expressed as (c/a).
10. The void fraction is the ratio of unfilled volume to total volume of a structure. For ideal metallic FCC crystal, it is:
a) 0.22
b) 0.26
c) 0.32
d) 0.38
Explanation: Void fraction = 1 − packing efficiency
Packing efficiency for FCC lattice is 0.74 and hence, void fraction is 1 − 0.74.