Copper crystallizes in $f.c.c.$ with a unit cell length of $361 \ pm$. What is the radius of copper atom? (in $pm$)

$(i)$ What is meant by the term 'coordination number'?
$(ii)$ What is the coordination number of atoms:
$(a)$ in a cubic close-packed structure?
$(b)$ in a body-centred cubic structure?

What is the volume occupied by particles in $BCC$ structure if '$a$' is the edge length of the unit cell?

$A$ unit cell of calcium fluoride has four calcium ions. The number of fluoride ions in the unit cell is

$A$ compound formed by elements $A$ and $B$ crystallizes in a cubic structure where $A$ atoms are at the corners of the cube and $B$ atoms are at the center of the cube. What is the formula of the compound?

Coordination numbers of $Zn^{2+}$ and $S^{2-}$ in the crystal structure of wurtzite are