The number of tetrahedral voids per unit $HCP$ cell is

The number of tetrahedral voids in the unit cell of a face-centered cubic $(fcc)$ lattice of similar atoms is:

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

The percentage of unoccupied volume in a simple cubic cell is (in $\%$)

The limiting radius ratio for a tetrahedral void is:

How many spheres form an octahedral void in a close-packed structure?