Solid State Question 163
Question: $ Na $ and $ Mg $ crystallize in BCC and FCC type crystals respectively, then the number of atoms of $ Na $ and $ Mg $ present in the unit cell of their respective crystal is
[AIEEE 2002]
Options:
A) 4 and 2
B) 9 and 14
C) 14 and 9
D) 2 and 4
Show Answer
Answer:
Correct Answer: D
Solution:
The bcc cell consists of 8 atoms at the corners and one atom at centre.
$ n=( 8\times \frac{1}{8} )+1=2 $ .
The fcc cell consists of 8 atoms at the eight corners and one atom at each of the six faces. This atom at the face is shared by two unit cells. $ n=8\times \frac{1}{8}+( 6\times \frac{1}{2} )=4 $ .
BETA
