Question

what is corrosion and give its cause of process

Answer 1

corrosion is a electro chemical that appears in several forms such as chemical corrosion,the latter of which the most common form.when acidic substances come in contact with metal like iron or steel rust begins to form

Answer 2

Corrosion refers to the attacking of a metal by any external factor such as air, water etc. which cause the destruction of the metal. 
Example- Rusting Of Iron