1. Most Bravais lattice are of the type:
a) Primitive unit cell
b) Body centered unit cell
c) End centered unit cell
d) Face centered unit cell
Answer: a [Reason:] Out of 14 naturally occurring Bravais lattices, 7 are primitive. Remaining seven consist of 3 body centered, 2 face centered and 2 end centered unit cells.
2. In which of the following Bravais lattices, not all axial angles are right angles?
Answer: b [Reason:] A rhombohedral is a prism whose base is shaped as a non-square rhombus. Hence two of its six faces are rhombuses while others are rectangles. This results in a geometry for which two of the axial angles are right angles but the third is not.
3. Which of the following Bravais lattices exist as face centered unit cell?
d) None of the mentioned
Answer: a [Reason:] Orthorhombic lattice exists as all four types of unit cells. Besides primitive cell, monoclinic lattice exists only as end centered cell while tetragonal exists only as body centered lattices.
4. Coordination number for an ideal BCC metallic crystal is:
d) Varies for different metals
Answer: a [Reason:] Consider the atom at the body center. It is touched by all the atoms present at the vertices of the cubic unit cell. We know that a cube has 8 vertices.
5. Number of particles in primitive cubic unit cell is:
Answer: 1 [Reason:] 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.
6. In which of the following Bravais lattices none of the sides are equal?
d) All of the mentioned
Answer: d [Reason:] 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.
7. Graphite is a common allotrope of Carbon. Its crystal structure is:
Answer: d [Reason:] 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.
8. 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
Answer: d [Reason:] Void fraction = 1 − packing efficiency
Since primitive cubic unit cell has least packing efficiency out of those mentioned above, hence it has highest void fraction of (1 − 0.52 = ) 0.48 or 48% .
9. 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
Answer: c [Reason:] Tetragonal lattices exist only in primitive and body centered unit cells. Face centered unit cells occur only for cubic and orthorhombic lattices.
10. Most unsymmetrical Bravais lattice in terms of axial distances and angles is:
Answer: b [Reason:] 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.
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