Here below some basic MCQ’s about “Solids, Unit cells and Packing Efficiency” with Answer explanation which is explained in details. Let’s check one by one which is given below.
1. Which of the following is a property of ionic solids?
a) High conductivity in solid state
b) High melting point
c) Malleability
d) High electrical conductivity in molten state
Answer:
d) High electrical conductivity in molten state
Explanation:
Ionic solids are composed of positive and negative ions held together by strong electrostatic forces. In their solid state, ions are fixed in place, and ionic solids do not conduct electricity. However, when molten or dissolved in water, the ions are free to move, allowing them to conduct electricity.
2. What is the coordination number of atoms in a body-centered cubic (BCC) unit cell?
a) 4
b) 6
c) 8
d) 12
Answer:
c) 8
Explanation:
In a body-centered cubic (BCC) structure, each atom at the corner of the unit cell is surrounded by 8 other atoms: one atom at the center of the unit cell and the rest are at the corners of adjacent unit cells. Hence, the coordination number is 8.
3. Which type of unit cell has atoms only at the corners?
a) Simple cubic
b) Face-centered cubic
c) Body-centered cubic
d) Hexagonal close-packed
Answer:
a) Simple cubic
Explanation:
In a simple cubic unit cell, atoms are located only at the corners of the cube. Each corner atom is shared among eight adjacent unit cells. This arrangement leads to a lower packing efficiency compared to other types of unit cells like face-centered cubic or body-centered cubic.
4. The packing efficiency of a face-centered cubic (FCC) structure is approximately:
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
c) 74%
Explanation:
In a face-centered cubic (FCC) structure, the atoms are packed more efficiently than in a simple cubic or body-centered cubic structure. The packing efficiency is about 74%, which means that 74% of the volume of the unit cell is occupied by atoms, and the remaining 26% is empty space.
5. What is the number of atoms per unit cell in a face-centered cubic (FCC) structure?
a) 1
b) 2
c) 4
d) 6
Answer:
c) 4
6. Which of the following unit cells has the highest packing efficiency?
a) Simple cubic
b) Body-centered cubic
c) Face-centered cubic
d) Hexagonal close-packed
Answer:
c) Face-centered cubic
Explanation:
The face-centered cubic (FCC) structure has a packing efficiency of 74%, which is the highest among the given options. Hexagonal close-packed (HCP) also has a packing efficiency of 74%, but since only cubic structures were compared, FCC is the answer.
7. In hexagonal close packing (hcp), what is the coordination number of each atom?
a) 4
b) 6
c) 8
d) 12
Answer:
d) 12
Explanation:
In hexagonal close-packed (hcp) structures, each atom is surrounded by 12 nearest neighbors: 6 atoms in the same plane, 3 atoms in the layer above, and 3 atoms in the layer below, making the coordination number 12.
8. Which of the following statements is true for molecular solids?
a) They conduct electricity in both solid and molten states
b) They have strong covalent bonds between molecules
c) They have relatively low melting points
d) They are always hard
Answer:
c) They have relatively low melting points
Explanation:
Molecular solids are held together by weak intermolecular forces such as van der Waals forces, dipole-dipole interactions, or hydrogen bonds. As a result, they typically have low melting points and do not conduct electricity.
9. The packing efficiency in a simple cubic structure is:
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
a) 52%
Explanation:
In a simple cubic structure, atoms occupy 52% of the total volume of the unit cell, and the remaining 48% is empty space. This is because atoms only occupy the corners of the cube, leading to a relatively low packing efficiency.
10. In a body-centered cubic (BCC) unit cell, what fraction of the total volume is occupied by atoms?
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
b) 68%
Explanation:
The packing efficiency of a body-centered cubic (BCC) structure is 68%, meaning 68% of the volume of the unit cell is occupied by atoms, and the rest is empty space.
11. Which of the following solids has a crystalline structure?
a) Glass
b) Rubber
c) Salt (NaCl)
d) Plastic
Answer:
c) Salt (NaCl)
Explanation:
Salt (NaCl) has a crystalline structure where the sodium and chloride ions are arranged in a regular, repeating pattern. This distinguishes it from amorphous solids like glass, rubber, and plastic, which do not have such ordered internal structures.
12. In a simple cubic unit cell, what fraction of each corner atom belongs to the unit cell?
a) 1
b) 1/2
c) 1/4
d) 1/8
Answer:
d) 1/8
Explanation:
In a simple cubic unit cell, each corner atom is shared by eight adjacent unit cells. Therefore, only 1/8 of each atom belongs to the unit cell.
13. What is the number of atoms per unit cell in a body-centered cubic (BCC) structure?
a) 1
b) 2
c) 4
d) 6
Answer:
b) 2
14. Which type of solid is known for being brittle and having high melting points?
a) Molecular solid
b) Ionic solid
c) Metallic solid
d) Covalent solid
Answer:
b) Ionic solid
Explanation:
Ionic solids, such as NaCl, are held together by strong electrostatic forces between positively and negatively charged ions. These forces give ionic solids high melting points and make them brittle, as any attempt to deform them causes the like charges to align and repel, causing the solid to break.
15. Which of the following unit cells is not a Bravais lattice?
a) Simple cubic
b) Body-centered cubic
c) Face-centered cubic
d) Tetragonal closed-packed
Answer:
d) Tetragonal closed-packed
Explanation:
There is no “tetragonal closed-packed” lattice. The correct terms for Bravais lattices include simple cubic, body-centered cubic, face-centered cubic, hexagonal, etc. The tetragonal lattice does exist, but it is either simple or body-centered, not “closed-packed.”
16. Which of the following statements is true for metallic solids?
a) They are good conductors of electricity
b) They have low melting points
c) They are poor conductors of heat
d) They are brittle
Answer:
a) They are good conductors of electricity
Explanation:
Metallic solids consist of positive metal ions surrounded by a “sea” of delocalized electrons, which can move freely. This free movement of electrons makes metallic solids good conductors of both electricity and heat. They are usually malleable and ductile, not brittle.
17. Which of the following is the correct packing efficiency for a simple cubic unit cell?
a) 74%
b) 52%
c) 68%
d) 100%
Answer:
b) 52%
Explanation:
The packing efficiency of a simple cubic unit cell is 52%, meaning that only 52% of the space in the unit cell is occupied by atoms, with the remaining 48% being empty space.
18. The coordination number of an atom in a face-centered cubic (FCC) structure is:
a) 4
b) 6
c) 8
d) 12
Answer:
d) 12
Explanation:
In a face-centered cubic (FCC) structure, each atom is surrounded by 12 nearest neighbors, giving it a coordination number of 12. This high coordination number contributes to the stability and close packing of FCC structures.
19. Which of the following solids is an example of a covalent (network) solid?
a) Diamond
b) Sodium chloride (NaCl)
c) Ice
d) Copper
Answer:
a) Diamond
Explanation:
Diamond is an example of a covalent or network solid. In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a rigid three-dimensional network. This structure gives diamond its characteristic hardness.
20. Which type of solid typically has the highest melting point?
a) Molecular solid
b) Ionic solid
c) Metallic solid
d) Covalent network solid
Answer:
d) Covalent network solid
Explanation:
Covalent network solids, such as diamond and silicon carbide, have the highest melting points because the atoms are connected by strong covalent bonds in a continuous network throughout the material.
21. In a hexagonal close-packed (hcp) structure, how many atoms are present in a single unit cell?
a) 4
b) 6
c) 8
d) 12
Answer:
b) 6
Explanation:
In a hexagonal close-packed (hcp) structure, each unit cell contains 6 atoms. These atoms are arranged in layers with a hexagonal arrangement, leading to efficient packing.
22. Which of the following solids is likely to dissolve in water and conduct electricity when molten?
a) Graphite
b) Sodium chloride (NaCl)
c) Sulfur
d) Diamond
Answer:
b) Sodium chloride (NaCl)
Explanation:
Sodium chloride (NaCl) is an ionic solid. It dissolves in water because the ions can separate and interact with water molecules. When molten, NaCl conducts electricity because the ions are free to move.
23. Which of the following best describes amorphous solids?
a) Have a well-defined geometric shape
b) Have long-range order
c) Have short-range order but lack long-range order
d) Are composed of ions arranged in a regular lattice
Answer:
c) Have short-range order but lack long-range order
Explanation:
Amorphous solids, such as glass, do not have a long-range ordered arrangement of their atoms. They may have short-range order, meaning that atoms or molecules are orderly only over short distances.
24. In an ionic solid, the magnitude of the lattice energy depends on:
a) The size of the ions
b) The charge on the ions
c) Both a and b
d) Neither a nor b
Answer:
c) Both a and b
Explanation:
The lattice energy of an ionic solid depends on both the charge of the ions and the size of the ions. A higher charge on the ions and smaller ionic radii result in a stronger electrostatic attraction and a higher lattice energy.
25. Which of the following has the highest packing efficiency?
a) Simple cubic
b) Body-centered cubic
c) Face-centered cubic
d) Tetragonal
Answer:
c) Face-centered cubic
Explanation:
The face-centered cubic (FCC) structure has a packing efficiency of 74%, which is higher than that of both simple cubic (52%) and body-centered cubic (68%) structures.
26. Which of the following statements is true about a crystal lattice?
a) A lattice point can be occupied by a single atom
b) The distance between two adjacent lattice points is called a unit cell
c) A unit cell is the smallest repeating unit in a crystal lattice
d) A crystal lattice is always amorphous
Answer:
c) A unit cell is the smallest repeating unit in a crystal lattice
Explanation:
The unit cell is the fundamental repeating unit in a crystal lattice. It defines the crystal structure by repeating in all three dimensions to form the entire lattice. Lattice points may contain atoms, ions, or molecules.
27. Which type of defect occurs when an atom or ion is missing from its regular lattice site in a crystal?
a) Interstitial defect
b) Vacancy defect
c) Frenkel defect
d) Schottky defect
Answer:
b) Vacancy defect
Explanation:
A vacancy defect occurs when an atom or ion is missing from its regular lattice position, creating a vacancy in the crystal structure. This type of defect decreases the density of the solid.
28. Which type of solid is characterized by a high melting point, hardness, and poor electrical conductivity in the solid state but good conductivity in the molten state?
a) Metallic solids
b) Ionic solids
c) Molecular solids
d) Covalent network solids
Answer:
b) Ionic solids
Explanation:
Ionic solids have high melting points and are hard due to the strong electrostatic forces between ions. In the solid state, they are poor conductors because the ions are fixed in place. However, in the molten state, they conduct electricity as the ions are free to move.
29. The effective number of atoms in a face-centered cubic (FCC) unit cell is:
a) 1
b) 2
c) 4
d) 6
Answer:
c) 4
30. The coordination number of a particle in a simple cubic structure is:
a) 4
b) 6
c) 8
d) 12
Answer:
b) 6
Explanation:
In a simple cubic unit cell, each particle is surrounded by 6 nearest neighbors: one on each of the six faces of the cube. Therefore, the coordination number is 6.
31. Which of the following is a type of defect found in ionic crystals where both cations and anions leave their lattice sites?
a) Frenkel defect
b) Vacancy defect
c) Schottky defect
d) Interstitial defect
Answer:
c) Schottky defect
Explanation:
A Schottky defect occurs in ionic crystals when equal numbers of cations and anions leave their lattice sites, creating vacancies. This defect reduces the density of the solid but maintains electrical neutrality.
32. Which of the following is a characteristic of amorphous solids?
a) Sharp melting points
b) Long-range order
c) Definite geometric shapes
d) Irregular arrangement of particles
Answer:
d) Irregular arrangement of particles
Explanation:
Amorphous solids lack a long-range ordered structure. Their particles are arranged randomly, unlike crystalline solids, which have a regular and repeating pattern. Amorphous solids do not have sharp melting points; they soften over a range of temperatures.
33. Which of the following shows metallic bonding?
a) Sodium chloride
b) Copper
c) Diamond
d) Ice
Answer:
b) Copper
Explanation:
Copper exhibits metallic bonding, where positive metal ions are surrounded by a “sea” of delocalized electrons that allow for high electrical and thermal conductivity. This contrasts with ionic bonding in sodium chloride or covalent bonding in diamond and ice.
34. What is the coordination number in a body-centered cubic (BCC) structure?
a) 4
b) 6
c) 8
d) 12
Answer:
c) 8
Explanation:
In a body-centered cubic (BCC) structure, each atom at the center of the cube is surrounded by 8 nearest neighbors at the corners of the cube, giving a coordination number of 8.
35. Which of the following solids conducts electricity due to the movement of electrons?
a) Ionic solids
b) Covalent network solids
c) Molecular solids
d) Metallic solids
Answer:
d) Metallic solids
Explanation:
Metallic solids conduct electricity due to the presence of free-moving delocalized electrons within the “sea of electrons.” In ionic solids, conduction occurs via ions in the molten state, while covalent network and molecular solids are generally poor conductors.
36. In which type of crystal defect do smaller ions occupy interstitial spaces in the crystal lattice?
a) Schottky defect
b) Vacancy defect
c) Interstitial defect
d) Frenkel defect
Answer:
c) Interstitial defect
Explanation:
In an interstitial defect, smaller atoms or ions occupy the spaces (interstices) between the regular lattice points. This type of defect increases the density of the crystal.
37. Which of the following has a hexagonal close-packed (hcp) structure?
a) Sodium
b) Iron
c) Zinc
d) Gold
Answer:
c) Zinc
Explanation:
Zinc has a hexagonal close-packed (hcp) structure, where the atoms are arranged in a hexagonal pattern with two layers of close-packed atoms. This structure has a coordination number of 12.
38. Which of the following types of solids is the best conductor of heat and electricity?
a) Ionic solid
b) Molecular solid
c) Metallic solid
d) Covalent network solid
Answer:
c) Metallic solid
Explanation:
Metallic solids are the best conductors of heat and electricity because of the presence of delocalized electrons that can move freely throughout the solid. These free electrons facilitate the conduction of electricity and heat.
39. Which of the following defects does not affect the density of the solid?
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Vacancy defect
Answer:
b) Frenkel defect
Explanation:
In a Frenkel defect, a smaller ion (usually a cation) leaves its normal lattice site and occupies an interstitial site. Since no ions are lost or gained, the overall density of the solid remains unchanged.
40. What is the type of bonding in diamond?
a) Metallic bonding
b) Ionic bonding
c) Covalent bonding
d) Hydrogen bonding
Answer:
c) Covalent bonding
Explanation:
Diamond consists of carbon atoms bonded covalently in a tetrahedral arrangement, forming a three-dimensional network. Each carbon atom is covalently bonded to four other carbon atoms, resulting in a very hard and strong structure.
41. Which of the following compounds forms a crystalline solid with a covalent network?
a) Sodium chloride
b) Graphite
c) Carbon dioxide
d) Ammonia
Answer:
b) Graphite
Explanation:
Graphite is a covalent network solid, where carbon atoms are arranged in layers of hexagonal rings. Each carbon atom is covalently bonded to three others in a single layer, and the layers are held together by weak van der Waals forces.
42. The packing efficiency in a body-centered cubic (BCC) structure is:
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
b) 68%
Explanation:
The packing efficiency of a body-centered cubic (BCC) structure is 68%, meaning that 68% of the space in the unit cell is occupied by atoms, and the remaining 32% is empty space.
43. The electrical conductivity of semiconductors increases with:
a) Decrease in temperature
b) Increase in temperature
c) Decrease in pressure
d) Increase in pressure
Answer:
b) Increase in temperature
Explanation:
The electrical conductivity of semiconductors increases with an increase in temperature. This is because heating a semiconductor provides more energy for electrons to jump from the valence band to the conduction band, resulting in higher conductivity.
44. The coordination number of an atom in a hexagonal close-packed (hcp) structure is:
a) 4
b) 6
c) 8
d) 12
Answer:
d) 12
Explanation:
In a hexagonal close-packed (hcp) structure, each atom is surrounded by 12 nearest neighbors—6 atoms in the same layer, 3 in the layer above, and 3 in the layer below. This results in a coordination number of 12.
45. Which of the following solids is classified as a molecular solid?
a) Sodium chloride
b) Copper
c) Iodine (I₂)
d) Diamond
Answer:
c) Iodine (I₂)
Explanation:
Iodine (I₂) is a molecular solid where individual iodine molecules are held together by weak van der Waals forces. It has low melting and boiling points compared to ionic, metallic, and covalent network solids.
46. The fraction of the volume occupied by atoms in a body-centered cubic (BCC) unit cell is:
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
b) 68%
Explanation:
In a body-centered cubic (BCC) structure, the packing efficiency is 68%. This means that 68% of the total volume of the unit cell is occupied by atoms, while 32% is empty space.
47. What is the type of defect called when a cation leaves its lattice site and moves to an interstitial position in the crystal?
a) Schottky defect
b) Frenkel defect
c) Vacancy defect
d) Interstitial defect
Answer:
b) Frenkel defect
Explanation:
A Frenkel defect occurs when a smaller ion, usually a cation, moves from its regular lattice site to an interstitial site, creating a vacancy at its original position while maintaining electrical neutrality.
48. Which of the following statements is true for covalent network solids?
a) They have high electrical conductivity
b) They are soft and have low melting points
c) They are hard and have high melting points
d) They have ionic bonds between their particles
Answer:
c) They are hard and have high melting points
Explanation:
Covalent network solids, such as diamond and quartz, consist of atoms covalently bonded in a continuous network. This strong bonding results in very high hardness and high melting points, making them different from molecular solids and ionic solids.
49. Which of the following is true about metallic solids?
a) They are brittle
b) They have high melting points and are malleable
c) They are poor conductors of electricity
d) They have sharp melting points
Answer:
b) They have high melting points and are malleable
Explanation:
Metallic solids have a characteristic structure where metal cations are surrounded by a “sea” of delocalized electrons. This gives them high melting points and makes them malleable and ductile, meaning they can be bent or shaped without breaking.
50. What is the number of atoms per unit cell in a hexagonal close-packed (hcp) structure?
a) 2
b) 4
c) 6
d) 8
Answer:
c) 6
Explanation:
A hexagonal close-packed (hcp) unit cell contains a total of 6 atoms. This is calculated based on contributions from the atoms at the corners, faces, and inside the unit cell.
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.
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.
71. The type of defect in ionic solids that reduces the overall density of the solid is:
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Vacancy defect
Answer:
a) Schottky defect
Explanation:
A Schottky defect occurs when equal numbers of cations and anions are missing from their lattice positions, creating vacancies. This defect reduces the density of the solid because mass is removed from the crystal without reducing its volume.
72. Which of the following materials would likely have the highest packing efficiency?
a) Diamond
b) Graphite
c) Sodium chloride
d) Copper
Answer:
d) Copper
Explanation:
Copper has a face-centered cubic (FCC) structure, which has a high packing efficiency of 74%. This is higher than the packing efficiencies of diamond, graphite, and sodium chloride, which have different types of structures.
73. Which of the following is true for molecular solids?
a) They have high melting points
b) They conduct electricity
c) They are hard and brittle
d) They are generally soft with low melting points
Answer:
d) They are generally soft with low melting points
Explanation:
Molecular solids are held together by weak intermolecular forces, such as van der Waals forces, leading to low melting points and softness. They do not conduct electricity and are not hard or brittle.
74. Which of the following statements is true about ionic solids?
a) They are malleable
b) They have high electrical conductivity in the solid state
c) They have high melting and boiling points
d) They are soft and flexible
Answer:
c) They have high melting and boiling points
Explanation:
Ionic solids have high melting and boiling points due to the strong electrostatic forces of attraction between oppositely charged ions. In the solid state, they do not conduct electricity, but they do conduct electricity when molten.
75. Which type of crystal defect is observed when cations move from their normal lattice positions to interstitial sites?
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Vacancy defect
Answer:
b) Frenkel defect
Explanation:
A Frenkel defect occurs when cations move from their normal lattice positions to interstitial sites within the crystal. This type of defect does not affect the overall density of the solid because no atoms are lost from the crystal.
76. Which of the following solids exhibits metallic bonding?
a) Sodium chloride
b) Diamond
c) Iron
d) Water
Answer:
c) Iron
Explanation:
Iron is a metallic solid that exhibits metallic bonding. In metallic solids, positive metal ions are surrounded by a sea of delocalized electrons that allow for electrical conductivity and malleability.
77. Which of the following has the least packing efficiency?
a) Simple cubic
b) Body-centered cubic (BCC)
c) Face-centered cubic (FCC)
d) Hexagonal close-packed (hcp)
Answer:
a) Simple cubic
Explanation:
Simple cubic structures have the least packing efficiency at approximately 52%. This is because the atoms are only arranged at the corners of the cube, leaving a lot of empty space compared to BCC (68%) and FCC or hcp (74%).
78. In which type of solid is the lattice composed of molecules held together by van der Waals forces?
a) Ionic solids
b) Molecular solids
c) Metallic solids
d) Covalent network solids
Answer:
b) Molecular solids
Explanation:
In molecular solids, molecules are held together by weak van der Waals forces, dipole-dipole interactions, or hydrogen bonds. These solids generally have low melting points and are poor conductors of electricity.
79. The crystal structure of a metal with a coordination number of 8 is most likely:
a) Simple cubic
b) Face-centered cubic (FCC)
c) Body-centered cubic (BCC)
d) Hexagonal close-packed (hcp)
Answer:
c) Body-centered cubic (BCC)
Explanation:
A body-centered cubic (BCC) structure has a coordination number of 8. Each atom in a BCC structure is surrounded by 8 nearest neighbors. In contrast, face-centered cubic (FCC) and hexagonal close-packed (hcp) structures have a coordination number of 12, while simple cubic has a coordination number of 6.
80. Which of the following is true about ionic solids?
a) They conduct electricity in the solid state
b) They have low melting points
c) They are soluble in polar solvents
d) They are malleable
Answer:
c) They are soluble in polar solvents
Explanation:
Ionic solids tend to dissolve in polar solvents like water because the polar molecules can interact with the ions and overcome the ionic bonds. Ionic solids do not conduct electricity in the solid state, but they do when molten or dissolved in a solvent.
81. Which type of defect involves the presence of extra atoms in the spaces between the regular lattice sites?
a) Frenkel defect
b) Schottky defect
c) Vacancy defect
d) Interstitial defect
Answer:
d) Interstitial defect
Explanation:
An interstitial defect occurs when extra atoms occupy the spaces (interstitial sites) between the regular lattice points in the crystal. This defect increases the density of the crystal since additional atoms are introduced without removing any.
82. The number of atoms in a hexagonal close-packed (hcp) unit cell is:
a) 2
b) 4
c) 6
d) 8
Answer:
c) 6
Explanation:
A hexagonal close-packed (hcp) unit cell contains 6 atoms: 2 atoms from the top and bottom hexagonal layers, and 3 atoms from the middle layer, along with 1 atom fully inside the unit cell.
83. Which of the following statements is true about metallic solids?
a) They are insulators
b) They are brittle
c) They are good conductors of heat and electricity
d) They are ionic in nature
Answer:
c) They are good conductors of heat and electricity
Explanation:
Metallic solids are characterized by a “sea of electrons” that are free to move throughout the structure, making them excellent conductors of both heat and electricity. They are also malleable and ductile, not brittle.
84. Which of the following elements forms a covalent network solid?
a) Sodium
b) Carbon (diamond)
c) Neon
d) Magnesium
Answer:
b) Carbon (diamond)
Explanation:
Diamond is an example of a covalent network solid, where carbon atoms are covalently bonded in a continuous, three-dimensional structure. This gives diamond its extreme hardness and high melting point.
85. In a crystal lattice, what is the term for the nearest neighboring particles surrounding a central particle?
a) Lattice point
b) Coordination number
c) Unit cell
d) Interstitial site
Answer:
b) Coordination number
Explanation:
The coordination number refers to the number of nearest neighboring particles surrounding a central particle in a crystal lattice. For example, in an FCC structure, the coordination number is 12.
86. Which of the following defects increases the electrical conductivity of a solid?
a) Schottky defect
b) Frenkel defect
c) Interstitial defect
d) Impurity defect
Answer:
d) Impurity defect
Explanation:
An impurity defect, where foreign atoms are introduced into the crystal lattice, can increase the electrical conductivity of a solid by providing additional charge carriers. This is the basis of semiconductor doping.
87. The coordination number of a simple cubic structure is:
a) 4
b) 6
c) 8
d) 12
Answer:
b) 6
Explanation:
In a simple cubic structure, each atom is surrounded by 6 nearest neighbors—4 in the same layer and 1 each above and below, giving a coordination number of 6.
88. Which type of crystal lattice has the highest packing efficiency?
a) Simple cubic
b) Body-centered cubic (BCC)
c) Face-centered cubic (FCC)
d) Tetragonal
Answer:
c) Face-centered cubic (FCC)
Explanation:
The face-centered cubic (FCC) lattice has the highest packing efficiency at 74%, which is greater than that of body-centered cubic (BCC) and simple cubic structures. This is because the atoms are packed more closely together in the FCC arrangement.
89. Which type of defect is created when an atom or ion is missing from its lattice site?
a) Frenkel defect
b) Schottky defect
c) Vacancy defect
d) Interstitial defect
Answer:
c) Vacancy defect
Explanation:
A vacancy defect occurs when an atom or ion is missing from its regular lattice site. This can affect the properties of the crystal, such as density and electrical conductivity.
90. Which of the following solids is likely to be a poor conductor of electricity?
a) Iron
b) Graphite
c) Diamond
d) Copper
Answer:
c) Diamond
Explanation:
Diamond is a covalent network solid where all the electrons are tightly bound in covalent bonds, leaving no free electrons to conduct electricity. This makes diamond an electrical insulator.
91. In which of the following structures do atoms occupy the octahedral voids?
a) Simple cubic
b) Face-centered cubic (FCC)
c) Body-centered cubic (BCC)
d) Hexagonal close-packed (hcp)
Answer:
b) Face-centered cubic (FCC)
Explanation:
In a face-centered cubic (FCC) structure, atoms or ions can occupy octahedral voids. These voids are located at the edge centers and at the body center of the unit cell.
92. Which of the following compounds forms an ionic crystal lattice?
a) Diamond
b) Silicon
c) Sodium chloride
d) Graphite
Answer:
c) Sodium chloride
Explanation:
Sodium chloride (NaCl) forms an ionic crystal lattice, where Na⁺ and Cl⁻ ions are held together by electrostatic forces in a repeating three-dimensional structure.
93. What is the fraction of the volume occupied by atoms in a face-centered cubic (FCC) unit cell?
a) 52%
b) 68%
c) 74%
d) 100%
Answer:
c) 74%
Explanation:
The packing efficiency of a face-centered cubic (FCC) unit cell is 74%, meaning that 74% of the unit cell’s volume is occupied by atoms, while the remaining 26% is empty space.
94. Which type of solid typically has the highest melting point?
a) Molecular solids
b) Ionic solids
c) Metallic solids
d) Covalent network solids
Answer:
d) Covalent network solids
Explanation:
Covalent network solids, like diamond and quartz, have very high melting points because the atoms are bonded together in an extended network of strong covalent bonds.
95. Which of the following defects can lead to the creation of color centers (F-centers) in a crystal?
a) Schottky defect
b) Frenkel defect
c) Vacancy defect
d) Interstitial defect
Answer:
c) Vacancy defect
Explanation:
Color centers, or F-centers, are created when an electron occupies a vacancy left by a missing anion in the lattice. This defect can absorb certain wavelengths of light, giving the crystal a color.
96. Which of the following types of solids generally has the lowest density?
a) Ionic solids
b) Metallic solids
c) Molecular solids
d) Covalent network solids
Answer:
c) Molecular solids
Explanation:
Molecular solids generally have the lowest density because they are held together by weak intermolecular forces, and the molecules are not as tightly packed as in ionic, metallic, or covalent network solids.
97. In a crystal lattice, tetrahedral voids are typically found in which structure?
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:
Tetrahedral voids are commonly found in both face-centered cubic (FCC) and hexagonal close-packed (hcp) structures. These voids are smaller than octahedral voids and are located between four atoms in the lattice.
98. Which of the following defects does not alter the overall electrical neutrality of a crystal?
a) Schottky defect
b) Frenkel defect
c) Impurity defect
d) Vacancy defect
Answer:
b) Frenkel defect
Explanation:
In a Frenkel defect, cations move from their regular lattice positions to interstitial sites, but no ions are lost from the lattice. Therefore, the overall electrical neutrality of the crystal remains unchanged.
99. In an ionic crystal, which type of defect results in the crystal becoming electrically conductive?
a) Schottky defect
b) Frenkel defect
c) Impurity defect
d) Vacancy defect
Answer:
c) Impurity defect
Explanation:
An impurity defect can introduce additional charge carriers into the crystal, which can increase the electrical conductivity. For example, doping an ionic crystal with ions of different valency can create free electrons or holes.
100. Which of the following statements is true for hexagonal close-packed (hcp) structures?
a) The coordination number is 8
b) The packing efficiency is lower than that of FCC
c) Each atom is surrounded by 12 neighbors
d) The structure has a simple cubic arrangement
Answer:
c) Each atom is surrounded by 12 neighbors
Explanation:
In a hexagonal close-packed (hcp) structure, each atom is surrounded by 12 nearest neighbors, giving it the same coordination number as in a face-centered cubic (FCC) structure. The packing efficiency is also 74%, the same as FCC.
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