Question

Which of the following statement(s) is/are correct?

• A. The coordination number of each type of ion in CsCl crystal is 8
• 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 $552\, pm$. $\left(r_{ Na ^{+}}=95 pm ; r_{ Cl ^{-}}=181 pm \right)$

Answer 1

Answer: (A), (C), (D)

(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; $2\left(r_{ Na ^{+}}+r_{ Cl ^{-}}\right)=a$
$\Rightarrow a=2(95+181)=552\, pm$