61. Which of the following is not a crystalline solid?
a) Quartz
b) Glass
c) Diamond
d) Sodium chloride
Answer:
b) Glass
Explanation:
Glass is an amorphous solid, meaning it does not have a regular or repeating arrangement of atoms, unlike crystalline solids like quartz, diamond, and sodium chloride.
62. Which of the following solids has a simple cubic structure?
a) Sodium chloride
b) Polonium
c) Copper
d) Magnesium oxide
Answer:
b) Polonium
Explanation:
Polonium crystallizes in a simple cubic structure, where atoms are located only at the corners of the unit cell. This structure is less common compared to body-centered and face-centered cubic structures.
63. In a crystal lattice, the position occupied by an atom, ion, or molecule is called:
a) Lattice point
b) Unit cell
c) Coordination number
d) Interstitial site
Answer:
a) Lattice point
Explanation:
A lattice point refers to the position in the crystal lattice where an atom, ion, or molecule resides. These points repeat periodically in a crystalline solid.
64. In a face-centered cubic (FCC) lattice, how many atoms are shared between adjacent unit cells at each face?
a) 1
b) 2
c) 4
d) 6
Answer:
b) 2
Explanation:
In a face-centered cubic (FCC) lattice, each face atom is shared between two adjacent unit cells. Therefore, only half of the face atom belongs to one unit cell, and the other half belongs to the adjacent unit cell.
65. Which of the following types of solids is expected to have the lowest melting point?
a) Metallic solids
b) Ionic solids
c) Molecular solids
d) Covalent network solids
Answer:
c) Molecular solids
Explanation:
Molecular solids have the lowest melting points because they are held together by weak intermolecular forces, such as van der Waals forces or hydrogen bonds, which are easier to overcome compared to the stronger bonds in metallic, ionic, and covalent network solids.
66. Which of the following is the most common packing arrangement in metals?
a) Simple cubic
b) Body-centered cubic (BCC)
c) Face-centered cubic (FCC)
d) Hexagonal close-packed (hcp)
Answer:
c) Face-centered cubic (FCC)
Explanation:
The face-centered cubic (FCC) arrangement is the most common packing arrangement in metals. It is efficient in terms of space utilization and results in a coordination number of 12. Examples of metals with an FCC structure include aluminum and copper.
67. Which of the following statements is true about defects in crystals?
a) Schottky defects occur in metals
b) Frenkel defects occur due to the dislocation of large ions
c) Schottky defects result in a decrease in density
d) Frenkel defects lead to an increase in density
Answer:
c) Schottky defects result in a decrease in density
Explanation:
In a Schottky defect, equal numbers of cations and anions leave their lattice sites, creating vacancies. This leads to a decrease in the overall density of the crystal. Frenkel defects do not affect density because ions only move to interstitial sites.
68. The coordination number of a particle in a face-centered cubic (FCC) structure is:
a) 4
b) 6
c) 8
d) 12
Answer:
d) 12
Explanation:
In an FCC structure, each particle is surrounded by 12 nearest neighbors, resulting in a coordination number of 12. This is the most efficient packing arrangement, giving FCC structures high packing efficiency.
69. The number of atoms in a body-centered cubic (BCC) unit cell is:
a) 1
b) 2
c) 4
d) 6
Answer:
b) 2
Explanation:
A body-centered cubic (BCC) unit cell contains 1 atom at the center of the cube and 8 atoms at the corners. Each corner atom contributes 1/8th of an atom to the unit cell, so the total number of atoms per BCC unit cell is:
1+(8×18)=21 + (8 \times \frac{1}{8}) = 21+(8×81)=2
70. Which type of solids is expected to conduct electricity in the molten state but not in the solid state?
a) Metallic solids
b) Ionic solids
c) Covalent network solids
d) Molecular solids
Answer:
b) Ionic solids
Explanation:
Ionic solids conduct electricity in the molten state because their ions are free to move and carry an electric charge. In the solid state, ions are fixed in place, and ionic solids do not conduct electricity.
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