What is the percentage of empty space in a $bcc$ unit cell (in $\%$)?

In a simple cubic lattice,what percentage of the space is left unoccupied by the spheres?

The volume occupied by the atoms in a unit cell of hexagonal close packing $(HCP)$ or cubic close packing $(CCP)$ is equal to:

What are the number of octahedral and tetrahedral voids in $0.3 \ mol$ of a substance respectively,if it forms an $hcp$ structure?

$A$ face-centred cubic $(FCC)$ unit cell is made up of two types of atoms $A$ and $B$,in which $A$ occupies the corner positions and $B$ occupies the face centres. If atoms along one of the body diagonals are removed,what is the empirical formula of the remaining solid?

$A$ compound is formed by $X$ and $Y$ elements. Atoms of $Y$ (anions) form $hcp$ lattice. Atoms of $X$ (cations) are in some octahedral holes. The formula of the compound is $XY_3$. What is the fraction of octahedral holes unoccupied by $X$?