Solid State - Result Question 28
####28. Which of the following statement(s) is/are correct?
(a) The coordination number of each type of ion in $CsCl$ crystal is 8
(1998, 2M)
(b) A metal that crystallises in bcc structure has a coordination number of 12
(c) A unit cell of an ionic crystal shares some of its ions with other unit cells
(d) The length of the unit cell in $NaCl$ is $552 pm$. $\left(r _{Na^{+}}=95 pm ; r _{Cl^{-}}=181 pm\right)$
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Answer:
Correct Answer: 28. $(a, c, d)$
Solution:
- (a) The unit cell of $CsCl$ has bcc arrangement of ions in which each ion has eight oppositely charged ions around it in the nearest neighbours as shown below :
(b) In bcc, coordination number of atom is 8 .
(c) In an unit cell, a corner is shared in eight unit cells and a face centre is shared between two adjacent unit cells.
(d) In $NaCl$ unit cell; $2\left(r _{Na^{+}}+r _{Cl^{-}}\right)=a$
$$ \Rightarrow \quad a=2(95+181)=552 pm $$
Hence, a, c, d are correct.
