The correct option is Black.
Explanation
Corrosion is the gradual degradation of metals due to chemical reactions with atmospheric gases such as oxygen, carbon dioxide, or sulfur. In the case of silver, this process is specifically known as tarnishing.
Detailed Analysis
Silver is a relatively unreactive metal; however, it is not completely immune to atmospheric corrosion. When exposed to air, silver reacts with sulfur-containing compounds, particularly hydrogen sulfide ($H_2S$).
- The chemical reaction produces silver sulfide ($Ag_2S$), which forms a coating on the surface of the metal.
- Silver sulfide is black in colour. Therefore, silver articles gradually turn black when left exposed to air for long periods.
Comparison with other common metals:
- Copper: Corrodes to form a green coating (patina) due to the formation of basic copper carbonate.
- Iron: Corrodes to form a reddish-brown powder known as rust (hydrated iron oxide).
Key Takeaway: The characteristic colour of corroded silver is black, caused by the formation of a layer of Silver Sulfide ($Ag_2S$).