What is the coordination number of a one-dimensional close-packed arrangement?

In an $A_{x} B_{y}$ crystal structure,$A$ atoms occupy all octahedral as well as all tetrahedral voids,and $B$ atoms are at the $FCC$ lattice points. What is the formula of the compound $A_{x} B_{y}$?

$A$ metal crystallises in a face-centred cubic $(fcc)$ structure. If the edge length of its unit cell is $a$,the closest approach between two atoms in the metallic crystal will be:

Calculate the packing efficiency in a simple cubic unit cell.

In an ionic solid compound,$A$ ions are at the corners of the cube and $B$ ions are at the center of each face. The molecular formula of the compound will be ..............

Explain the calculation of packing efficiency in $hcp$ and $ccp$ structures with the help of a diagram.