What is the coordination number in a hexagonal close-packed $(h.c.p.)$ structure?

In a face-centered cubic arrangement of $A$ and $B$ atoms,$A$ atoms are at the corners of the unit cell and $B$ atoms are at the face centers. If one of the $B$ atoms is missing from one of the faces in the unit cell,the simplest formula of the compound is:

The coordination number of an atom in a body-centered cubic $(BCC)$ structure is:
[Assume that the lattice is made up of atoms.]

Structure similar to zinc blende is found in

For $bcc$ cubic coordination the value of radius ratio is

If the edge length of a cubic unit cell is $a$,then the octahedral void is located at a distance of ....... from the corner of the cube.