Define the following terms in relation to crystalline solids: (i) Unit cell

(i) Unit cell: A unit cell is the smallest portion of a crystal lattice which, when repeated in different direction, generates the entire lattice.

(ii) Coordination number: The number of nearest neighbours of any constituent particle in a packing is called its coordination number. The coordination number of an atom in the bcc structure is 8.

i) Unit Cell:- Smallest element of a crystal lattice which on repetition gives the entire crystal lattice.  Eg - cubic unit cell

ii) Coordination Number  :- The number of neighbour atoms attached to a central atom         Eg - In hcp the C.N is 6 (three dimensional)