Question

Why do silver jewellery becomes black after sometime, whereas silver does not react easily with oxygen?

Answer 1

Answer:

due to the action of silver sulphide

silver does not react with oxygen as it is less reactive and can react only with sulphur

Answer 2

Silver jewelries often becomes black or tarnishes after certain period of continuous use. This process of silver turning black may look like iron rusting of oxidation; but, it is not. Silver doesn't react with oxygen. So, there will not be any oxidation reaction to turn the silver black.

The real reason for the silver to turn black is its reaction with Sulphur in the air. Silver can easily react with Sulphur in the air. Usually, that much of sulphur gas  was produced by humans by burning fossil fuels like coal.

Apart from the sulphur, there are other reasons too. Silvers action with soap, ground water that has chemical contamination and others.