What is the coordination number of a particle in a simple cubic structure?

The coordination number of a metal crystallizing in a hexagonal close packed structure is

What is the nature of octahedral holes (voids)?

Which statement is not correct?

$Xe$ crystallizes in an $fcc$ structure. If the edge length of the unit cell of $Xe$ is $620 \, pm$, then the distance between two nearest $Xe$ atoms is .............. $pm$.

What is the coordination number in a calcium fluoride $(CaF_2)$ type structure?