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

In a face-centred cubic $(FCC)$ unit cell,what fraction of the edge length is not covered by the constituent atoms?

The interionic distance for $Cesium$ $chloride$ $(CsCl)$ crystal will be (where $a$ is the edge length of the unit cell):

In the rock salt structure,the number of formula units per unit cell is equal to

In a face-centered cubic $(FCC)$ lattice,$A$ atoms are present at the corners and $B$ atoms are present at the face centers. If one $B$ atom is removed from one of the face centers,what will be the molecular formula of the compound?

The unit cell of a $NaCl$ lattice: