What is the percentage of unoccupied space in $fcc$ unit cell (in $\%$)?

Give two examples of metals that crystallize in the $hcp$ (hexagonal close-packed) structure.

What is the percentage of space occupied in a $bcc$ arrangement (in $\%$)?

Which of the following statements is correct for an $fcc$ lattice?

For a simple cubic $(SC)$,body-centered cubic $(BCC)$,and face-centered cubic $(FCC)$ unit cell with edge length $a$,what is the ratio of the radii of the atoms present in them?

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