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.
Leave a comment