What does the term tarnish refer to?

The term "tarnish" primarily refers to the process of a surface, especially metals like silver, becoming dulled or discolored as a result of exposure to air or moisture, which leads to oxidation. This definition aligns well with the idea of making something dirty or unclean, specifically in a way that results from environmental factors. In a broader sense, such tarnishing can also metaphorically imply that something has been negatively affected or "dirtied," sometimes in a moral or mental way. This understanding highlights how exposure to external elements can lead to deterioration or a loss of luster, which is exactly what option B describes.

The other options do not accurately represent the term. Polishing to a shine is the opposite of tarnishing, while decorating with colors and preserving for a long time do not relate to the inherent concept of tarnishing, which is about degradation over time.