Unit cell is the smallest three-dimensional repeating unit in a crystal lattice, it generates the entire lattice, when it is repeated in different directions. Unit cell defines the geometry of the whole crystal lattice.

Void can be defined the unoccupied empty space in a unit cell or empty space in the unit cell. Voids are also known as holes in the unit cell. Voids in solid states mean the vacant space between the constituent particles in a closely packed structure.

What type of stoichiometric defect is shown by ZnS ?

Frenkel defect or dislocation defect is observed in Zinc sulphide. This defect arises due to the hole in cationic lattice site and the cation occupying an interstitial position. This is because the size of the cation, i.e Zinc, is smaller than the anion and hence it occupies the interstitial site leaving behind a hole or vacant.