Engineering Questions with Answers - Multiple Choice Questions
Materials Science MCQ’s – Properties of Crystals
1 - Question
Allotropes differ in which of the following properties:
a) Atomic Number
b) Atomic Mass
c) Crystal Structure
d) Electronegativity
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Explanation: Allotropes are different crystalline structures of the same element. Hence, they have the same atomic number, atomic mass and electronegativity. For e.g., graphite and diamond are allotropes of carbon.
2 - Question
Co-ordination number of a crystalline solid is:
a) Number of particles in the unit cell
b) Number of nearest neighbours of a particle
c) Number of octahedral voids in a unit cell
d) Number of tetrahedral voids in a unit cell
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Explanation: Coordination number of a crystal structure is the number of particles with which a given particle is in direct contact.
3 - Question
Packing efficiency of a crystal structure is the ratio of:
a) Volume occupied by particles to the total volume of the unit cell
b) Volume occupied by particles to that by voids
c) Total volume of the unit cell to the volume occupied by particles
d) Volume occupied by voids to that by particles
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Explanation: Packing efficiency represents the fraction of the unit cell volume that is utilized to hold the particles.
4 - Question
HCP and BCC are called close-packed structures. Close packed structures have:
a) Highest packing efficiency
b) Highest void fraction
c) Highest density
d) All of the mentioned
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Explanation: Due to the largest number of particles in a unit cell, close-packed structures have the highest packing efficiency and hence, lest void fraction. Density is NOT a property of the crystal structure but the substance and depends also on molar mass.
5 - Question
An octahedral void is surrounded by:
a) 8 atoms
b) 18 atoms
c) 6 atoms
d) 16 atoms
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Explanation: An octahedral void resembles a regular octahedron with atoms situated at all the six vertices.
6 - Question
Which of the following is a property of amorphous solids?
a) Sharp melting point
b) Isotropy
c) Long range order
d) Definite heat of fusion
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Explanation: Due to irregularity in structure, the average of physical properties like density, thermal and electrical conductivity etc. is same along any direction for a particular amorphous solid.
7 - Question
Which of the following is a crystalline solid?
a) Copper wire
b) Glass bottle
c) Polythene bag
d) Rubber ball
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Explanation: Copper wires are made of crystalline copper. In fact, most metallic objects are crystalline. However, research for the large-scale production of amorphous metals is in progress.
8 - Question
The smallest portion of a crystal which when repeated in different directions generates the entire crystal is called:
a) Lattice points
b) Crystal lattice
c) Unit cell
d) None of the mentioned
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Explanation: Unit cell is the smallest unit of a crystal which repeats itself to generate the crystal. Lattice point represents the centres of atoms in a unit cell. Crystal lattice refers to the entire structure of a crystalline solid.
9 - Question
Which of the following is not a property of metal glass?
a) Transparent
b) Poor thermal conductivity
c) High magnetic susceptibility
d) None of the mentioned
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Explanation: Metal glass is a form of metal which like glass, is amorphous but not transparent. Most of the metal glasses are alloys, having high yield strength and high elastic strain limits. High magnetic susceptibility, low coercivity and comparatively higher electrical resistance than their crystalline counterparts make them an ideal material for power transformers.
10 - Question
Grain boundaries are one of the causes of corrosion of metals?
a) True
b) False
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Explanation: Grain boundaries are the regions that separate two grains in polycrystalline metallic solids. The absence of properly defined structure results in residual stresses. Hence, grain boundaries are the weak spots in the structure and are often the site of a fracture.