In antifluorite structure,the negative ions

In a face-centred cubic $(FCC)$ unit cell,what is the total volume occupied by the atoms?

If a compound (oxide) has an $hcp$ arrangement and the cations $M$ occupy two-thirds of the octahedral voids,the formula of the compound is:

The percentage of vacant space for $bcc$ unit cell is ............. $\%$

In a face-centred cubic $(FCC)$ lattice,where are the tetrahedral voids located?

$A$ compound is formed by two elements $A$ and $B$. The element $B$ forms a cubic close-packed $(CCP)$ structure and atoms of $A$ occupy $\frac{1}{3}$ of the tetrahedral voids. If the formula of the compound is $A_x B_y$,then the value of $x+y$ is: