Answer: Face-centred cubic.
- A Simple cubic
- B Body-centred cubic
- C Face-centred cubic
- D Orthorhombic
Correct answer: C. Face-centred cubic
Explanation: Both FCC (ccp) and HCP achieve the maximum packing efficiency of 74%, higher than SC (52.4%) or BCC (68%).
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.