JEE Advanced · 2016 · 22 May 2016 · Paper 2 · Solid State

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

(A)The number of the nearest neighbours of an atom present in the topmost layer is 12
(B)The efficiency of atom packing is 74%✓ Correct
(C)The number of octahedral and tetrahedral voids per atom are 1 and 2, respectively✓ Correct
(D)The unit cell edge length is $22$ times the radius of the atom✓ Correct

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

Solution

In ccp (fcc), atoms in the middle layers have 12 nearest neighbors, but atoms in the topmost layer have only 9 nearest neighbors. The packing efficiency is 74%. There is 1 octahedral void and 2 tetrahedral voids per atom. The face diagonal is

4 r

and equals

a 2

, so

a = 22 r

JEE Advanced · 2016 · 22 May 2016 · Paper 2 · One or more correct options

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