$A$ student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of black and green coatings.

(N/A) The chemical phenomenon responsible for these coatings is $Corrosion$.
Silver coins develop a black coating of $Silver \text{ } Sulphide$ $(Ag_2S)$ due to the reaction with sulphur compounds present in the air.
Copper coins develop a green coating of $Basic \text{ } Copper \text{ } Carbonate$ $(CuCO_3 \cdot Cu(OH)_2)$ due to the reaction with moist carbon dioxide and oxygen in the air.