Solid State Question 140
Question: How many molecules are there in the unit cell of sodium chloride
[MP PMT 1996; MP PET 1997]
Options:
A) 2
B) 4
C) 6
D) 8
Show Answer
Answer:
Correct Answer: B
Solution:
In $ NaCl $ (rock salt) : Number of $ N{{a}^{+}} $ ions $ =12 $ (at edge centers) $ \times \frac{1}{4}+1 $ (at body centre) $ \times 1=4 $ .
Number of $ C{{l}^{-}} $ ions $ =8 $ (at corners) $ \times \frac{1}{8}+6 $ (at face centre) $ \times \frac{1}{2}=4 $ . Thus 4 formula units per unit cell.
BETA
