What are crystal defects?

Crystal defects refer to imperfections or irregularities that occur in the orderly arrangement of atoms within a crystalline structure. In a perfect crystal, atoms are arranged in a highly organized and repeating pattern; however, in real-world materials, this perfect order is often disrupted. These imperfections can occur in various forms, including vacancies (missing atoms), interstitials (extra atoms within the structure), and dislocations (misalignments in the arrangement), among others.

Understanding crystal defects is essential for various applications in materials science and engineering, as they can significantly influence the physical properties of the material, such as its strength, conductivity, and reactivity. This makes option C the most accurate definition, as it highlights the presence of imperfections in crystalline structures, which is crucial for understanding material behavior.

The other options do not accurately capture the essence of crystal defects. Perfect structures with no flaws would indicate an ideal scenario that does not exist in practice; patterns of light reflection do not inherently describe crystal defects but rather refer to optical properties; and uniform arrangements of atoms would imply the absence of any defects, contradicting the concept itself.