Option (c) becoz--->
Silver articles when exposed to air become black after sometime. This is because the silver metal reacts with sulphur present in the atmosphere and forms silver sulphide (black colour).

Ag (s) + H2S (g) → Ag2S (s) + H2 (g)

Why do silver articles become black on prolonged exposure to air?

The blackening of silver articles on prolonged exposure to air is due to the formation of a layer of silver sulfide (Ag2S) on the surface of the silver. This is a chemical reaction that occurs between the silver and sulfur compounds in the air.

Explanation:

- Chemical Reaction: The reaction between silver and sulfur compounds in the air is a chemical reaction that results in the formation of silver sulfide. The reaction can be represented by the following equation: 2Ag + H2S + O2 → Ag2S + H2O
- Formation of Silver Sulfide: The silver sulfide that forms on the surface of the silver is a black compound that gives the silver article its black appearance. Silver sulfide is insoluble in water, which means it cannot be easily removed from the surface of the silver.
- Air Pollution: The reaction between silver and sulfur compounds in the air is accelerated by air pollution. Sulfur dioxide (SO2) is a common air pollutant that can react with silver to form silver sulfide. This is why silver articles tend to blacken more quickly in areas with high levels of air pollution.
- Prevention: The blackening of silver articles can be prevented by storing them in airtight containers or by using anti-tarnish strips. These strips contain chemicals that react with sulfur compounds in the air, preventing them from reacting with the silver. Regular cleaning and polishing can also help to prevent the formation of silver sulfide on the surface of silver articles.

Conclusion:

In conclusion, the blackening of silver articles on prolonged exposure to air is due to the formation of a layer of silver sulfide on the surface of the silver. This is a chemical reaction that occurs between the silver and sulfur compounds in the air. The reaction can be prevented by storing silver articles in airtight containers, using anti-tarnish strips, and regular cleaning and polishing.