51. The structure of a diamond is an example of:
a) Ionic crystal
b) Molecular crystal
c) Covalent network crystal
d) Metallic crystal
Answer:
c) Covalent network crystal
Explanation:
Diamond is a covalent network crystal, where each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral structure. This strong bonding gives diamond its extreme hardness and high melting point.
52. Which of the following statements is true about crystalline solids?
a) They have irregular shapes
b) They have sharp melting points
c) They lack long-range order
d) They soften over a range of temperatures
Answer:
b) They have sharp melting points
Explanation:
Crystalline solids have a well-defined and regular arrangement of particles, which gives them a sharp melting point, unlike amorphous solids that soften over a range of temperatures.
53. Which of the following represents a molecular solid held together by hydrogen bonds?
a) Ice (H₂O)
b) Sodium chloride
c) Diamond
d) Copper
Answer:
a) Ice (H₂O)
Explanation:
Ice is a molecular solid where water molecules are held together by hydrogen bonds. Hydrogen bonding is a type of strong intermolecular force that gives ice its structure and properties.
54. In which type of defect does the density of the crystal decrease?
a) Frenkel defect
b) Schottky defect
c) Interstitial defect
d) None of the above
Answer:
b) Schottky defect
Explanation:
In a Schottky defect, equal numbers of cations and anions leave their lattice positions, creating vacancies. This results in a decrease in the density of the crystal because mass is lost without a corresponding decrease in volume.
55. The edge length of a unit cell of a body-centered cubic structure is 300 pm. What is the radius of the atom?
a) 100 pm
b) 150 pm
c) 200 pm
d) 260 pm
Answer:
b) 150 pm
56. Which of the following solids has the highest melting point?
a) Sodium chloride
b) Diamond
c) Iodine
d) Sulfur
Answer:
b) Diamond
Explanation:
Diamond, a covalent network solid, has extremely strong covalent bonds throughout its structure, giving it an exceptionally high melting point compared to other types of solids.
57. Which type of unit cell is not part of the Bravais lattice system?
a) Simple cubic
b) Face-centered cubic
c) Rhombohedral
d) Tetragonal closed-packed
Answer:
d) Tetragonal closed-packed
Explanation:
The term “tetragonal closed-packed” does not exist in the Bravais lattice system. The correct term would be “tetragonal,” but it is not closed-packed. The Bravais lattice includes simple cubic, face-centered cubic, body-centered cubic, and other well-defined types.
58. Which of the following solids would exhibit the greatest electrical conductivity?
a) Diamond
b) Sodium chloride (solid)
c) Graphite
d) Ice
Answer:
c) Graphite
Explanation:
Graphite conducts electricity due to the presence of delocalized electrons within its layered structure. Unlike diamond, where all electrons are localized in covalent bonds, graphite has free electrons that allow it to conduct electricity.
59. Which of the following defects increases the density of a crystal?
a) Schottky defect
b) Frenkel defect
c) Vacancy defect
d) Interstitial defect
Answer:
d) Interstitial defect
Explanation:
An interstitial defect occurs when extra atoms or ions occupy positions between the regular lattice points. This increases the mass of the crystal without increasing its volume, thus increasing the density.
60. Which of the following is not an example of an ionic solid?
a) NaCl
b) MgO
c) Diamond
d) CaF₂
Answer:
c) Diamond
Explanation:
Diamond is a covalent network solid, not an ionic solid. The other choices, NaCl, MgO, and CaF₂, are ionic solids consisting of cations and anions held together by electrostatic forces.
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