How will you distinguish between the following pairs of terms?
a. Hexagonal close-packing and cubic close-packing
b. Crystal lattice and unit cell
c. Tetrahedral void octahedral void

Explanation

(i)
(ii) The three dimensional arrangement of constituent particles of a substance (atoms, ions or molecules) is called crystal lattice.
The smallest repeating pattern in a crystal lattice which when repeated in three dimensions gives the crystal is called unit cell.
(iii) A void surrounded by four spheres is called a tetrahedral void while a void surrounded by six spheres is called an octahedral void.