Which of the following metals has an $hcp$ crystal structure?

In a binary compound,atoms of element $A$ form a $hcp$ structure and those of element $M$ occupy $2/3$ of the tetrahedral voids of the $hcp$ structure. The formula of the binary compound is

The structure of a mixed oxide is cubic close packed $(ccp)$. The cubic unit cell of the mixed oxide is composed of oxide ions. One-fourth of the tetrahedral voids are occupied by divalent metal $A$ and the octahedral voids are occupied by a monovalent metal $B$. The formula of the oxide is:

In a $ccp$ arrangement,what is the number of octahedral voids per atom?

What does a tetrahedral void in a crystal represent?

If the number of tetrahedral voids in a crystal lattice is $N$,then the number of close-packed spheres will be ..........