What is the coordination number of a particle in $hcp$ structure?

The unit cell of a $NaCl$ lattice:

The crystal $AB$ has a structure similar to $NaCl$. Atoms of $A$ are present at each corner of the cubic unit cell. If all atoms along one of the axes passing through the face centers are removed,what will be the resulting stoichiometry?

$A$ certain metal crystallizes in a $bcc$ lattice. The distance between the nearest neighbours is $433 \text{ pm}$. The distance between the next nearest neighbours is :- .............. $\text{pm}$

The crystal structure of the solid compound $XY$ is similar to $NaCl$. If the radius of the cation $X^+$ is $100 \, pm$, then the radius of the anion $Y^-$ will be ......... $pm$.

What is the coordination number of the $hcp$ crystal lattice?