The number of octahedral void$(s)$ per atom present in a cubic close-packed structure is

What is the percentage of void space in $hcp$ and $ccp$ structures (in $\%$)?

Which of the following statements is not correct?

How many tetrahedral voids are present in $0.4 \ mol$ of a compound that forms an $hcp$ structure?

In the $fcc$ structure, the number of tetrahedral holes per sphere is

$A$ compound is formed by two elements $A$ and $B$. Atoms of the element $B$ (as anion) make $ccp$ lattice and those of element $A$ (as cation) occupy all tetrahedral voids. The formula of the compound is