Which of the following best explains why metals are shiny?

• A. Metals have a rough surface that scatters light in all directions.
• B. The atoms in metals absorb all incident light.
• C. Metals contain large amounts of water that refract light.
• D. The free electrons in metals reflect light at the surface.

Answer: (D)

Verified step by step guidance

1. Understand that the shininess of metals is related to how they interact with light at the atomic level.
2. Recall that metals have free or 'delocalized' electrons that are not bound to any specific atom and can move freely throughout the metal lattice.
3. Recognize that when light (which is an electromagnetic wave) hits the surface of a metal, these free electrons can oscillate in response to the electric field of the light.
4. These oscillating free electrons then re-emit or reflect the light waves, causing the metal surface to appear shiny and reflective.
5. Contrast this with other options: rough surfaces scatter light, absorption of all light would make the metal appear dark, and water content is not relevant to metallic luster.