Though there are many solids taking face-centered cubic unit cell, the number of solids adopting body-centered cubic unit cell decreases significantly and the number of solid adopting primitive cubic unit cell is even smaller.
Using Coordination numbers and intermolecular forces and energy to explain. Please and thanks
For the answer to the question above, because fcc is highly effective and packed structures! It leaves only 26℅ of free space, while bcc leaves 32 and simple is 47.6 ℅ only. So fcc is mostly found. I hope this helps you with tour problem
