What is the minimum value of the radius ratio ${r_ + }/{r_ - }$ for $NaCl$ to ensure that anion-anion contact does not occur?

In a solid $AB$,$A$ atoms are in $ccp$ arrangement and $B$ atoms occupy all the octahedral sites. If two atoms from the opposite faces are removed,then the resultant stoichiometry of the compound is $A_{x} B_{y}$. The value of $x$ is ..... [nearest integer]

In a hexagonal close packing $(hcp)$ lattice,each sphere touches ................... spheres in its own layer.

If $Z$ is the number of atoms in the unit cell that represents the closest packing sequence $ABCABC$,the number of tetrahedral voids in the unit cell is equal to

Diamond has a three-dimensional structure of $C$ atoms formed by covalent bonds. The structure of diamond has a face-centered cubic $(FCC)$ lattice where $50\,\%$ of the tetrahedral voids are also occupied by carbon atoms. The number of carbon atoms present per unit cell of diamond is $......$

What is the coordination number of $Cs^{+}$ and $Cl^{-}$ ions in the $CsCl$ structure?