Answer: 6.
- A 2
- B 6
- C 4
- D 12
Correct answer: B. 6
Explanation: The hcp unit cell contains 6 atoms (12 corners x 1/6 + 2 face centres x 1/2 + 3 interior). Its packing efficiency is 74%, the same as ccp/fcc.
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.