Give two examples of metals that crystallize in the $hcp$ (hexagonal close-packed) structure.

In a metal oxide,$O^{2-}$ ions are arranged in $hcp$ lattice while metal ions occupy $2/3$ of the octahedral voids. The simplest formula of the oxide is:

In a compound,atoms of element $Y$ form $ccp$ lattice and those of element $X$ occupy $2/3$ of tetrahedral voids. The formula of the compound will be

For a simple cubic $(SC)$,body-centered cubic $(BCC)$,and face-centered cubic $(FCC)$ unit cell with edge length $a$,what is the ratio of the radii of the atoms present in them?

Explain close packing in one dimension. Explain close packing in two dimensions.

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