Answer: 6 and 3.
- A 4 and 4
- B 6 and 3
- C 8 and 4
- D 12 and 6
Correct answer: B. 6 and 3
Explanation: If B forms FCC (4 B per cell), there are 4 octahedral voids and A fills all of them. The ratio A:B = 4:4 = 1:2. Each A has CN = 6 (octahedral); each B has CN = 3 (one A has 6 B but the reverse: each B is surrounded by 3 A).
The three cubic unit cells: Simple Cubic has atoms only at corners; Body-Centred adds one atom at the centre; Face-Centred adds one atom at the centre of each of the 6 faces, giving the highest packing efficiency.
Concept context
Explore the ordered world of crystalline solids: unit cells, packing, defects, and how structure determines electrical and magnetic properties.