Chemistry - Solid State Question with Solution | TestHub

Solution:

A. Packing fraction for 2D square close packing is $\frac{\pi }{4}$. This is correct.

B. Packing fraction for 2D hexagonal close packing is $\frac{\pi }{2\sqrt{3}}$. This is correct.

C. An octahedral void is formed by six spheres, but its shape is not a perfect regular octahedron. This is incorrect.

D. The radius ratio ($r/R$) for an octahedral void in close-packed structures (HCP/CCP) is 0.414. This is the maximum radius of an atom that can fit without distortion. This is correct.

Therefore, options A, B, and D are correct.