In $FCC$,the distance between the nearest tetrahedral voids is:

Atom $X$ occupies the $fcc$ lattice sites as well as alternate tetrahedral voids of the same lattice. The packing efficiency (in $\%$) of the resultant solid is closest to

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

Which crystal lattice has the maximum packing efficiency?

Hexagonal close packed arrangement of ions is described as

In an ionic solid,anions $(B)$ are arranged in a $ccp$ array and cations $(A)$ occupy $1/3$ of the tetrahedral voids. What is the formula of the ionic compound?