Why does silver turn black when exposed to air? 

Due to the formation of silver sulphide

The correct answer is option 1. Due to the formation of silver sulphide.

Silver turns black when exposed to air primarily due to the formation of silver sulfide \((Ag_2S)\).

When silver is exposed to air containing hydrogen sulfide \((H_2S)\) or sulfur-containing compounds, such as sulfur dioxide \((SO_2)\) or sulfur compounds in the atmosphere, it undergoes a chemical reaction with sulfur to form silver sulfide. This reaction can be summarized as follows:

\[ \text{2Ag} (s) + \text{H}_2\text{S} (g) \rightarrow \text{Ag}_2\text{S} (s) + \text{H}_2 \]

In this reaction, silver reacts with hydrogen sulfide gas to form black silver sulfide \((Ag_2S)\), which appears as a dark tarnish on the surface of the silver metal. This tarnish layer can darken over time, resulting in the characteristic black appearance observed on tarnished silver objects.

While silver chloride, silver carbonate, and silver nitride can also form under certain conditions, they are not the primary compounds responsible for the blackening of silver when exposed to air. Silver sulfide, due to its dark color, is the main compound responsible for the black tarnish observed on silver surfaces.