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

Options

A. The number of neighbours of an atom present in the topmost layer is 12
B. The efficiency of the 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 `2sqrt2` times the radius of the atom

Answer

B,C,D

Explanation

(a) is incorrect because for any atom in the top most layer, coordination number is not 12 as there is no layer above the topmost layer.
(b ) is a known fact.
(c ) is correct because in ccp (fcc), number of atoms per unit cell is 4. hence , octahedral voids =4 and tetrahedral voids=8. Therefore , number of octahedral voids per atom =1 and number of tetrahedral voids per atom =2.
(d)For ccp (fcc), `r=a/(2sqrt2)` or `a=2sqrt2r`