chemistry : class12 Face-Centred Cubic Structure : Crystalline solids : Solid State MCQ Questions and Answers
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Face-Centred Cubic Structure
MCQ questions and answers.
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MCQ Questions
1. How many atoms are effectively present in one face-centred cubic unit cell?
A.
1
B.
2
C.
4
D.
6
Correct Answer:
4
Explanation:
An FCC unit cell has 8 corner atoms, each contributing one-eighth, and 6 face-centred atoms, each contributing one-half. Thus, total atoms = 8 × 1/8 + 6 × 1/2 = 4.
2. In a face-centred cubic unit cell, atoms are present at which positions?
A.
Corners only
B.
Corners and body centre
C.
Corners and face centres
D.
Face centres only
Correct Answer:
Corners and face centres
Explanation:
In an FCC structure, atoms occupy all eight corners and the centre of each of the six faces of the cubic unit cell.
3. What is the coordination number of an atom in a face-centred cubic structure?
A.
4
B.
6
C.
8
D.
12
Correct Answer:
12
Explanation:
Each atom in an FCC structure is surrounded by 12 nearest neighbouring atoms, so its coordination number is 12.
4. What fraction of an atom located at a face centre belongs to one FCC unit cell?
A.
One-eighth
B.
One-fourth
C.
One-half
D.
Entire atom
Correct Answer:
One-half
Explanation:
A face-centred atom is shared equally between two adjacent unit cells. Therefore, one-half of the atom belongs to a particular FCC unit cell.
5. Which relationship between edge length a and atomic radius r is valid for an FCC unit cell?
A.
a = 2r
B.
a = 2√2r
C.
a = √2r
D.
a = 4r
Correct Answer:
a = 2√2r
Explanation:
In an FCC structure, atoms touch along the face diagonal. The face diagonal is √2a and contains four radii, so √2a = 4r, giving a = 2√2r.
6. What is the packing efficiency of a face-centred cubic structure?
A.
52.4%
B.
68%
C.
74%
D.
84%
Correct Answer:
74%
Explanation:
The FCC arrangement has a packing efficiency of 74%, meaning that 74% of the unit-cell volume is occupied by atoms.
7. How many atoms are located at the faces of an FCC unit cell?
A.
4
B.
6
C.
8
D.
12
Correct Answer:
6
Explanation:
An FCC unit cell has one atom at the centre of each of its six faces.
8. Which of the following metals commonly has a face-centred cubic structure?
A.
Copper
B.
Sodium
C.
Potassium
D.
Cesium
Correct Answer:
Copper
Explanation:
Copper has an FCC crystal structure. Sodium, potassium, and cesium commonly have body-centred cubic structures.
9. In an FCC unit cell, how many corner atoms effectively contribute to one unit cell?
A.
1
B.
2
C.
4
D.
8
Correct Answer:
1
Explanation:
There are 8 corner atoms, and each is shared by 8 unit cells. Therefore, their total contribution is 8 × 1/8 = 1 atom.
10. Along which part of an FCC unit cell do the atoms touch each other?
A.
The edge of the cube
B.
The body diagonal
C.
The face diagonal
D.
The vertical axis only
Correct Answer:
The face diagonal
Explanation:
In an FCC unit cell, atoms touch along the face diagonal. This gives the relation √2a = 4r between the edge length and atomic radius.
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Face-Centred Cubic Structure
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