Question

The correct statement(s) for cubic close packed (ccp) three dimensional structure is/are:

• A. The number of the nearest neighbours for an atom present in the topmost layer is 12.
  
• B. The efficiency of atom packing is 74%.
• C. The number of octahedral and tetrahedral voids per atom are 1 and 2, respectively.
• D. The unit cell edge length is $2\sqrt{2}$ times the radius of the atom.

Answer 1

Answer: (B), (C), (D)

The unit cell edge length is $2\sqrt{2}$ times the radius of the atom.

The middle layers will have 12 nearest neighbours. The top-most layer will have 9 nearest neighbours.
$4r=a\sqrt{2},$ where ‘a’ is edge length of unit cell and ‘r’ is radius of atom. Thus $a=2\sqrt{2}r$.