What physical characteristic do crystalline solids exhibit?

Crystalline solids are characterized by their highly ordered arrangement of atoms or molecules, which forms a repeating pattern throughout the material. This ordered structure is what leads to a defined melting point. In these solids, the specific arrangement of particles allows them to bond in a uniform way, resulting in a precise temperature at which the solid will transition into a liquid. This is in contrast to amorphous solids, which do not have a defined structure and therefore do not exhibit a clear melting point; instead, they gradually soften over a range of temperatures.

The other physical characteristics mentioned do not apply to crystalline solids in the same way. For example, random structure would describe amorphous solids, while high compressibility is not a typical feature of crystalline materials, as they tend to be less compressible due to their regular arrangement. High electrical conductivity can occur in some crystalline materials, like metals, but it is not a defining characteristic of all crystalline solids. Thus, having a defined melting point is the fundamental attribute that distinguishes these materials.