Question

The number of atoms contained in one face-centred cubic unit cell of monoatomic substance is:

• A. $1$
• B. $2$
• C. $4$
• D. $3$

Answer 1

The correct option is C $4$

The number of atoms contained in one face-centred cubic unit cell of monoatomic substance is 4.
8 atoms are present at 8 corners of a fcc unit cell. Each atom contributes one eigth to the unit cell. Total contribution $=8\times \frac{1}{8}=1$
6 atoms are present at 6 corners of a fcc unit cell. Each atom contributes one half to the unit cell. Total contribution $=6\times \frac{1}{2}=3$
Total number of atoms in one fcc unit cell $=1+3=4$.