Final answer:
Crystalline Order is the best description for the careful ordering of molecules within solids that have a fixed shape.
Step-by-step explanation:
The careful ordering of molecules within solids that have a fixed shape is best described as Crystalline Order. Crystalline solids have a regular arrangement of their particles, which is reflected in the macroscopic level. The attractive interactions between particles are maximized, and the total intermolecular energy is minimized when the particles pack in the most efficient manner.