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(B) In an $FCC$ unit cell,the number of atoms per unit cell $(Z)$ is $4$.The relationship between edge length $(a)$ and atomic radius $(r)$ is $a = 2\

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$\pi / 3\sqrt{2}$

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(B) In an $FCC$ unit cell,the number of atoms per unit cell $(Z)$ is $4$.The relationship between edge length $(a)$ and atomic radius $(r)$ is $a = 2\sqrt{2}r$.The volume of $4$ atoms is $4 	imes (\frac{4}{3} \pi r^3) = \frac{16}{3} \pi r^3$.The volume of the unit cell is $a^3 = (2\sqrt{2}r)^3 = 16\sqrt{2}r^3$.Packing fraction = $\frac{	ext{Volume of atoms}}{	ext{Volume of unit cell}} = \frac{\frac{16}{3} \pi r^3}{16\sqrt{2}r^3} = \frac{\pi}{3\sqrt{2}}$.

In a face-centered cubic $(FCC)$ structure,the fraction of the total volume occupied by atoms is .... ($a =$ edge length)

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