Final answer:
A crystal structure with a resolution below 2.0 Ångstroms is considered very good because at this scale, atomic and molecular structures can be accurately determined.
Step-by-step explanation:
When evaluating the resolution of a crystal structure, a resolution below 2.0 Ångstroms (A) is usually considered to be very good. This is because the angstrom, which is equivalent to 10-10 meters, is a natural unit for describing atomic and molecular scale structures. When a crystal structure is resolved to this level of detail, the positions of the atoms within the crystal lattice can be determined with a high degree of accuracy.