Corrosion a chemical reaction that involves: 

Corrosion is a degradation process of metal surfaces. The metal is oxidized into an oxide when exposed to atmospheric air and vapours. Thus it is a surface phenomenon and it does not change to another element but to a compound.

Corrosion is a naturally occurring process in which the physical and chemical characteristics of the refined metal are altered and the metal transforms into a more stable form, such as oxides, sulphides, or possibly hydroxides.
Numerous factors might cause corrosion. Prolonged exposure to air that contains a mixture of various gases is the key component at play.
We frequently observe rusting of iron in our daily lives. Iron oxide, a chemical that is reddish brown in colour, is created when the metal iron combines with oxygen and moisture in the air. In addition to typical corrosion, electrochemical corrosion also happens.
As a result, the iron surface basically experiences corrosion, changing from an element to a compound.

Hence, the correct answer is option C.