UPSC CDS 1 2021 GK Paper

The silver article becomes black after reacts with sulfur which is present in the atmosphere. Then sulfur forms silver sulfide on the surface of the silver article, so they appear as dull or black. This layer of silver sulfide can be removed by rubbing the article with toothpaste because toothpaste consists of several abrasive substances like Aluminum hydroxide that makes silver metal all shiny.