Question

In NaCl structure :
Options are-
(A) all octahedral and tetrahedral sites are occupied
(B) only octahedral sites are occupied
(C) only tetrahedral sites are occupied
(D) neither octahedral or tetrahedral sites are occupied

Answer 1

An attempt to this question can be made by recalling the structure of NaCl. Determine the position of sodium ions and chlorine ions. Based on this you can determine the ions present in voids and the composition of the voids as well. Based on this you can determine the correct option and answer the question.

Complete answer:
We will determine the structure of NaCl crystals as suggested in the hint.

The black atoms correspond to ${Cl^-}$ ions and white atoms correspond to ${Na^+}$ atoms.
In the structure we see that chlorine ions are present in all the corners. On the other hand, sodium ions occupy the octahedral voids. In the structure we see that all of the octahedral voids are occupied.
From the above statements we can conclude that in In NaCl structure only octahedral sites are occupied.

Therefore, the correct answer is option (B).

Note:
It should be remembered to you that on application of high pressure, The NaCl structure changes to CsCl structure whereas on heating the CsCl structure at 760K, the CsCl structure transforms to NaCl structure.
The structure of CsCl is given below:

The grey atoms correspond to ${Cl^-}$ ions and black atom is ${Cs^+}$ ion.
Also, you should remember that CsCl is used in isopycnic centrifugation for separating various types of DNA.