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JEE Main levelOne or more correct optionsDifficulty 2 of 3ss122

Which of the following statements about cubic close packing (ccp) of identical spheres are correct?

AThe coordination number of each sphere is 12.
BThere are 4 spheres per unit cell.
CThe packing efficiency is about 74%.
DThe unit cell edge is $a = 4 r / 3$ .

Answer: A, B, C

ccp is the fcc lattice: CN

= 12

,

Z = 8 \times \frac{1}{8} + 6 \times \frac{1}{2} = 4

, efficiency

= 74%

. The edge is

a = 22 r

;

4 r / 3

applies to bcc, so only A, B, C are correct.

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