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What is the packing efficiency of a body-centred cubic (bcc) lattice of identical atoms?

A68%
B52%
C74%
D32%

Answer: A

In bcc, 2 atoms per cell and atoms touch along the body diagonal, so

a = 4 r / 3

. Packing efficiency

= 2 \times \frac{4}{3} π r^{3} / a^{3} \approx 0.68

, i.e. 68%.

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