Concept:The shiny appearance of metals is produced by the behaviour of electrons at the surface.
Explanation:In a metal, the outermost electrons are not tied to any particular atom.
These electrons move freely through the whole metallic structure.
They are known as delocalised or free electrons.
When light falls on a metal surface, these free electrons absorb the light energy.
The electrons then re-emit the light immediately.
This absorption and re-emission causes the light to be reflected strongly.
That strong reflection makes the metal appear bright and lustrous.
High density, refractive density, and chemical inertness are not responsible for metallic shine.
The characteristic lustre of a metal is directly due to the presence of free electrons.
Answer:D. free electrons