Crystal Imperfections — Defects from Imperfect Atomic Packing Which defect is specifically associated with imperfect packing at discrete atomic sites during crystallisation?

Introduction / Context:
Real crystals are never perfect. Defects profoundly influence mechanical, electrical, and diffusion properties. Understanding the taxonomy of defects helps interpret strengthening mechanisms, diffusion paths, and fracture behavior.

Given Data / Assumptions:

• Crystallisation leads to imperfect atomic packing.
• Interest is in defects localized at single lattice sites.
• Standard classifications: point, line, and surface defects.

Concept / Approach:
Point defects occur at or around one lattice point and include vacancies (missing atoms), interstitials (extra atoms in interstitial sites), and substitutional solutes. Line defects are dislocations (edge/screw/mixed) spanning along a line, while surface defects include grain boundaries, stacking faults, and free surfaces. Imperfect local packing produced during solidification first manifests as point defects; dislocations and grain boundaries reflect larger-scale mismatches.

Step-by-Step Solution:
Identify the scale of imperfection: discrete atomic positions → point scale.Map to classification: vacancy/interstitial/substitutional → point defects.Exclude line (dislocations) and surface (boundaries) as extended defects.

Verification / Alternative check:
Diffusion kinetics and electrical resistivity changes correlate strongly with point defect concentrations generated during quenching or radiation.

Why Other Options Are Wrong:
Line defects represent long-range mismatches, not single-site packing errors.Surface defects are two-dimensional interfaces, not discrete site imperfections.“None of these/volume defect only” does not match the described origin.

Common Pitfalls:
Confusing stacking faults (planar) with point defects; stacking faults are surface/planar defects.

Final Answer:
point defect