Question

The number of carbon atoms per unit cell of diamond unit cell is:

• A. $4$
• B. $8$
• C. $6$
• D. $1$

Answer 1

The correct option is B $8$

Diamond has fcc unit cell structure made up of atoms.

This accounts for $8\times \frac{1}{8}+6\times \frac{1}{2}=1+3=4$ $C$ atoms
C atoms are also present in one half of the tetrahedral voids.

There are $8$ tetrahedral voids in fcc structure.
This accounts for remaining $8\times \frac{1}{2}=4$ $C$ atoms
Thus, total $4+4=8$ C atoms are present per unit cell of diamond.