Chemical Reactions and Equations — Science STD 10 — Question

1. Silver article turns black when kept in the air because silver article reacts with sulphur compounds such as hydrogen sulphide (H₂S) present in air. The phenomenon is called corrosion. For silver particularly, it is called tarnishing of silver.
2. The black substance formed is silver sulphide (ag₂s). 

$2\text{Ag}\ \ \ \ +\ \ \ \ \ \ \ \text{H}_2\text{S}\xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Ag}_2\text{S}\ \ \ \ \ \ \ \ +\ \ \ \ \ \ \text{H}_2\\^\text{Silver}\ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Hydrogen}\ \ \ \ \ \ \ \ \ \ \ ^\text{ Silver}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{ Hydrogen}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Sulphide }\ \ \ \ \ \ \ \ \ \ \ ^\text{sulphide}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(black)}$