Question

Number of atoms in the unit cell of $Na(BCC$ type crystal) and Mg (FCC type crystal) are respectively :

• A. 4,4
• B. 4,2
• C. 2,4
• D. 1,1

Answer 1

Answer: (C)

Na unit cell (body centred cubic)

8 corner atoms $\times \frac{1}{8}=1$

1 atom placed inside the unit cell $=1$

Total atoms $=2$

Mg unit cell (Face centred cubic)

8 corner atoms $\times \frac{1}{8}=1$

6 face atoms $\times \frac{1}{2}=3$

Total atoms $=4$