Question

The rusting of metals by contact and chemical union with oxygen in the damp atmosphere is known as:
A. corrosion
B. sublimation
C. oxidation
D. none of the above

Answer 1

Metal surfaces have a tendency to react with oxygen, especially in damp conditions to form more stable compounds of the metal, like oxides. This leads to the destruction of the smoothness and structural quality of the metal’s surface, and parts of it disintegrate.

Complete step by step answer:
Metals naturally have a tendency to react with oxygen. In moist conditions, this tendency increases, and metals combine with oxygen to produce their respective oxides. These oxides form as a layer over the surface and are deposited as a brownish red substance, commonly known as rust. Oxygen has a tendency to abstract electrons from a metal’s surface. Thus, moisture laden air increases the rate of rusting as oxidation occurs at a faster rate. Although the underlying process involved is oxidation, the correct name given for the formation of rust over metals is ‘corrosion’.
Hence, the correct option to be marked in this question is option A.

Additional information: Rusting/corrosion can be prevented using a number of methods, the most popular of which is galvanization. Galvanization involves coating the metal surface with one or more layers of zinc. The zinc in this case acts as a sacrificial metal. That is, it gets itself oxidised so that the oxygen is prevented from reaching the metal surface beneath.

Note: Apart from moisture, temperature also increases the rate of corrosion. As a general rule, every ten degree rise in temperature doubles the rate of corrosion. Also, note that when the metal cools below the temperature of the surrounding air, moisture condenses on the metal’s surface and this too increases the rate of corrosion. Corrosion is a highly undesirable characteristic and thus, use of materials like stainless steel, which do not corrode, are used to make industrial machinery.