What is the coordination number of the $Ca^{2+}$ ion in the fluorite structure?

$A$ crystal is made of particles $X$ and $Y$. $X$ forms $fcc$ packing and $Y$ occupies all the octahedral voids. If all the particles along one body diagonal are removed,then the formula of the crystal would be:

Which of the following statements is incorrect for the rock salt type structure?

In a body-centered cubic $(BCC)$ unit cell,the atom at the body center is shared by how many unit cells?

$Na$ and $Mg$ crystallise in $b.c.c.$ and $f.c.c.$ type crystals respectively. The number of atoms of $Na$ and $Mg$ present in the unit cell of their respective crystals is:

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