Question

The coordination number of a metal crystallizing in a hexagonal close packed (hcp) structure is:

• A. 5
• B. 4
• C. 8
• D. 12

Hint:

Both hcp and fcc (cubic close packing) have a coordination number of 12, which represents maximum packing efficiency.

Answer 1

The Correct Option is D

Step 1: Recall definition.
The coordination number is the number of nearest neighbours surrounding a particle in a crystal lattice.
Step 2: hcp structure.
In hexagonal close packing, each atom is surrounded by 12 equidistant atoms (6 in the same layer, 3 above, and 3 below).
Step 3: Conclusion.
Thus, the coordination number in hcp is 12.