Which term defines any set of parallel and evenly spaced planes distributed along certain crystal directions in which atoms are more closely packed?

• A. Crystal Planes
• B. Crystal Systems
• C. Glassie
• D. Defect

Answer: (A)

Lattice planes describe flat, evenly spaced sheets that slice through a crystal along specific directions. A set of parallel planes where the atoms sit most densely is a crystal plane family, defined by the arrangement of atoms in those planes. In crystallography these are simply called crystal planes, often indexed by Miller indices to indicate their orientation. This fits the description because it emphasizes parallel, evenly spaced planes and regions of higher atomic packing along certain directions.

Crystal systems, by contrast, refer to the overall symmetry and lattice parameters of the crystal rather than the individual plane families. Glassie isn’t a standard crystallography term, and a defect describes irregularities in the lattice rather than the regular, closely packed planes themselves.