. The co ordination number of the cation in the Face
centered cubic(FCC) lattice is:
The Face centered cubic lattice has unit cells in which the constituent particles are placed at each corner and at the center of each face center.
The coordination number is referred to as the number of atoms that are nearest to an atom in the crystalline structure.
The coordination number is also referred to as the nearest neighbour.
Considering one of the cations placed at the face center, we can see that it is surrounded by 4 corner atoms of its own plane and 8 adjacent face centered atoms (4 from each unit cell) (as marked in the figure below).
Thus, every atom is surrounded by 12 other atoms and the coordination number is 12.
Hence, the correct answer is option D: 12.