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. $(r_{Na^+} = 95pm; r_{Cl^-} = 181pm$

Answer 1

Answer: (D)

The length of the unit cell in NaCl is 552 pm. $(r_{Na^+} = 95pm; r_{Cl^-} = 181pm$

Answer 2

(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 comer is shared in eight unit cells and a face centre is shared between two adjacent unit cells.
(d) In NaCI unit cell; $2(r_{Na^+} + r_Cl^- ) = a$ $\Rightarrow \, \, \, a = 2(95 + 181) = 552pm$ Hence, a, c, d are correct.