Chemistry - Solid State Question with Solution | TestHub

In a hexagonal close-packed (hcp) structure, each constituent particle is in direct contact with $6$ neighboring particles in its own layer.

Additionally, it touches $3$ particles in the layer immediately above it and $3$ particles in the layer immediately below it.

Therefore, the total coordination number of a particle in an hcp structure is $6+3+3=12$.

Answer: 12