Answer: 1.633.
- A 1.414
- B 1.633
- C 1.732
- D 2.000
Correct answer: B. 1.633
Explanation: For an ideal HCP (hard spheres of equal size touching), the c/a ratio is sqrt(8/3) = 1.633. Metals with c/a close to this value (e.g., Mg = 1.624) approach ideal packing.
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.