Solid State Question 278
Question: The radii of $ N{{a}^{+}} $ and $ C{{l}^{-}} $ ions are 95 pm and 181 pm respectively. The edge length of $ NaCl $ unit cell is
Options:
A) 276 pm
B) 138 pm
C) 552 pm
D) 415 pm
Show Answer
Answer:
Correct Answer: C
Solution:
[c] In a fcc lattice, the distance between the cation and anion is equal to the sum of their radii, which is equal to half of the edge length of unit cell, i.e. $ ~{{r}^{+}}+{{r}^{-}}=\frac{a}{2} $ (where a = edge length) $ {{r}^{+}}=95pm,{{r}^{-}}=181pm $ Edge length $ =2{{r}^{+}}+2{{r}^{-}}=(2\times 95+2\times 181)pm $
$ =( 190+362 )pm=552pm. $
BETA
