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:

  1. (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.



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