In HCP arrangement of atoms, coordination no. of atoms in the middle layer is …         

(7)

For  structure,  of

Number of /unit cell (corner + face center)

Number of /unit cell (in alternate TVs)

Number of  ion removed

 (Two from each face center)  (per face center share) = 2

Number of  ions left /unit cell

Number of  ions entering in place of

[To maintain electrical neutrality, ]

Formula