# Mechanical Behaviour Questions and Answers – Basics of Crystal Structures

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Basics of Crystal Structures”.

1. What is true for FCC crystal structure?
a) a√2 = 4r
b) a√3 = 4r
c) a = 2r
d) a√2 = 2r

Explanation: For FCC unit cell, a√2 = 4r because face centered atom touches the corner atoms located at the face. a√3=4r is true for BCC unit cell and a = 2r for a simple cubic unit cell.

2. What is true for BCC unit cell?
a) a√2=4r
b) a√3=4r
c) a=2r
d) a√3=2r

Explanation: For BCC unit cell, a√3=4r because body centered atom touches all the corner atoms. While a√2=4r is in the case of FCC unit cell and a=2r is true for a simple cubic unit cell.

3. Which metal has a diamond cubic structure?
a) Ti
b) α-Sn
c) α-Fe
d) Os

Explanation: Ti and Os have HCP crystal structure. α-Sn has a diamond cubic structure while α-Fe is BCC.

4. Which metals has a BCC crystal structure?
a) Li, Na, K
b) Be, Zn, Cd
c) Li, Al, Ca
d) As, Cr, Bi

Explanation: Lithium, sodium and potassium all are BCC structure while beryllium, zinc, cadmium are HCP. Aluminum, calcium are FCC and arsenic and bismuth are rhombohedral.

5. Which metals have an FCC crystal structure?
a) Cu, Pt, Ag
b) Mo, Nb, Rb
c) Au, Os, Hg
d) As, Sb, Bi

Explanation: Copper, platinum and silver all have FCC structure. Gold(Au) has FCC structure but osmium, mercury are HCP and Mo, Nb, Rb are BCC and As, Sb, Bi are rhombohedral.
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6. Effective number of atoms for FCC is ______________
a) 2
b) 4
c) 6
d) 1

Explanation: 8 atoms sharing 1/8 part in corners and 6 atoms sharing 1/2 part on faces. 8(1/8) + 6(1/2) = 4

7. Effective number of atoms for HCP is ___________
a) 6
b) 4
c) 2
d) 1

Explanation: In HCP structure there are 6 atoms sharing 1/6 part at two corners, 2 atoms at the face centers sharing 1/2 part and 3 atoms at the center of the cell. 12(1/6) + 2(1/2) + 3 = 6

8. c/a ratio for HCP is _____________
a) 1.633
b) 0.816
c) 1.05
d) 0.74

Explanation: For HCP structure c = 1.633a so c/a ratio is 1.633. Packing factor for HCP is 0.74.

9. Coordination number for BCC structure is _______________
a) 8
b) 12
c) 2
d) 6

Explanation: In BCC structure, one atom touches 8 neighboring atoms which are known as coordination number. 12 is coordination number for FCC crystal structure.

10. Coordination number for FCC structure is __________
a) 6
b) 2
c) 8
d) 12

Explanation: In FCC structure one atom touches 12 neighboring atoms which makes it ductile structure. 8 is coordination number for BCC crystal structure.

11. Representation of family of planes is ______________
a) (h k l)
b) {h k l}
c) [h k l]
d) < h k l >

Explanation: Family of planes is represented as { h k l } where h, k and l are integers while a plane is denoted as (h k l).

12. Representation of family of directions is _____________
a) (h k l)
b) { h k l }
c) [h k l]
d) < h k l >

Explanation: Family of directions is represented as < h k l > where h, k and l are integers while a direction is denoted as [h k l].

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