Question

Total number of particles i.e. $\left(Z_{eff}\right)$ in a 3-D hexagonal close packed (hcp) unit cell is

Answer 1

For a HCP unit cell :


Contribution for :
$\text{Corner particles of two hexagonal layers}=12\times \frac{1}{6}=2$
$\text{Centre particles of two hexagonal layers}=2\times \frac{1}{2}=1$
$\text{Particles of middle layer}=3\times 1=3$

$\text{No. of particles in an HCP unit cell}=2+1+3=6$