Which of the following metals crystallizes in a hexagonal close-packed $(hcp)$ structure?

When sodium is heated above $1000 \ K$,its crystal structure changes from $bcc$ to $fcc$. Assuming the metallic radius of the atom remains unchanged,the ratio of the fraction of volume occupied by atoms in $bcc$ and $fcc$ structures will be .......

In which of the following crystals are all the tetrahedral voids occupied?

Find the void volume of $fcc$ unit cell in $cm^3$ if the volume of $fcc$ unit cell is $1.25 \times 10^{-22} \ cm^3$.

The correct option for the number of tetrahedral and octahedral voids in a hexagonal primitive unit cell is:

What is the number of octahedral voids present in $0.2 \ mol$ of a compound forming $hcp$ structure?