ANS:B - a chemical phenomenon.

Corrosion is a chemical phenomenon. Corrosion refers to the degradation of a material, typically a metal, as a result of chemical reactions with its environment. These reactions involve the loss of electrons from the metal atoms, leading to the formation of compounds such as oxides, hydroxides, or salts. Corrosion can occur through various mechanisms, including oxidation, reduction, and dissolution, depending on the specific conditions and the type of metal involved. Unlike erosion, which is a physical process involving the mechanical wearing away of a material by friction or impact, corrosion involves chemical changes in the material's structure. Corrosion is also distinct from erosion in that it can occur even in the absence of mechanical forces, solely as a result of chemical interactions between the material and its surroundings. While corrosion can sometimes be controlled or mitigated through preventive measures such as coatings, inhibitors, or cathodic protection, it is not inherently uncontrollable. However, it can be challenging to completely eliminate corrosion in many practical applications due to the complex and diverse nature of the corrosion process.