Question

For a solid with the following structure, the coordination number of the solid spheres (A) and the hollow spheres (B) respectively are:

• A. 6, 8
• B. 8, 8
• C. 6, 6
• D. 4, 6

Answer 1

The correct option is C 6, 6

The given structure is similar to that of $NaCl$ in which coordination number of each $N{a}^{+}$ and $C{l}^{-}$ ions is 6.

You can also visualise this by looking at the solid sphere in the centre, it is surrounded by 6 hollow spheres, 4 in plane, 1 above it and one below the plane, giving us a cordination number 6.

If you look at the corner hollow sphere, you can see 3 solid spheres on the edge centres, similarly, neighbouring unit cells would have 3 more such solid spheres giving us a cordination number 6.