 How many atoms per unit cell does a **face-centred cubic** (FCC) structure contain?
A8
B4
C2
D1
Answer & Solution
Correct answer: B. 4
FCC has atoms at:
- 8 corners, each contributing $1/8$ → $8 \times 1/8 = 1$
- 6 face centres, each contributing $1/2$ (shared between 2 cells) → $6 \times 1/2 = 3$
Total: $1 + 3 = 4$ atoms per unit cell.
Compare with BCC ($1 + 1 = 2$), simple cubic (1), and HCP (typically 6 per unit cell).
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