If the circles represent molecules, which diagram provides the best molecular level representation of a pure solid in the process of melting?

Molecular Representation of a Pure Solid During Melting

The best molecular-level representation of a pure solid during melting is diagram B.

Molecular Behavior During Melting

• Solid state: Molecules are closely packed in a fixed, ordered arrangement, vibrating in place but not moving freely.
• Melting transition: As thermal energy increases, molecular vibrations intensify until intermolecular forces are partially overcome. This causes localized breakdown of the crystalline structure, allowing molecules to slide past each other while remaining in close proximity.
• Key visual characteristics:
  • Partial retention of ordered regions (solid-like).
  • Increased intermolecular spacing compared to a full solid.
  • Molecules exhibit transitional mobility—more dynamic than a solid but less chaotic than a liquid.

Why Diagram B?

Diagram B accurately depicts this transitional state by showing:

• Ordered clusters (indicating residual solid structure).
• Moderate intermolecular spacing (wider than a solid but narrower than a gas).
• Directional movement (suggesting initial sliding motion without full liquid dispersal).

Contrast with Other Diagrams

• Diagram A: Represents a rigid, fully ordered solid (no melting occurring).
• Diagram C/D: Shows high disorder or large intermolecular gaps, characteristic of liquids or gases, not a melting solid.

Conclusion: Diagram B best captures the coexistence of residual order and increasing molecular mobility during melting.