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NEET levelSingle correct optionDifficulty 1 of 3ss111

The packing efficiency of a cubic close packed (face-centred cubic) arrangement of identical spheres is

A68%
B74%
C52%
D26%

Answer: B

In ccp,

Z = 4

and the spheres touch along the face diagonal, so

a = 22 r

. Packing fraction

= \frac{4 \times \frac{4}{3} π r ^{3}}{( 2 2 r ) ^{3}} = \frac{π}{3 2} \approx 0.74

, i.e. 74%.

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