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

The crystal structure of $AB$ is of $NaCl$ type. If the radius of the $A^+$ ion is $x \ pm$ and the radius of the $B^-$ ion is $y \ pm$, then the edge length of the unit cell will be ..........

What is the crystal structure of $Na_2O$?

The crystal structure of the solid compound $XY$ is similar to $NaCl$. If the radius of the cation $X^+$ is $100 \, pm$, then the radius of the anion $Y^-$ will be ......... $pm$.

The structure of $TlCl$ is similar to $CsCl$. What is the coordination number of $Tl^{+}$?

The coordination number of a metal crystallizing in a hexagonal close-packed $(hcp)$ structure is: