(a) Define corrosion.

(b) What is corrosion of iron called?

(c) How will you recognise the corrosion of silver?

(d) Why corrosion of iron is a serious problem?

(e) How can we prevent corrosion?

(a) Corrosion: Corrosion is the slow, progressive degradation and eating up of a metal's surface due to its chemical reaction with atmospheric gases, moisture, or acids.

(b) Corrosion of iron: The corrosion of iron is specifically called rusting.

(c) Corrosion of silver: Silver corrosion is recognized by the formation of a black coating on the surface of silver articles when exposed to air, which is due to the formation of silver sulphide ($\text{Ag}_2\text{S}$).

(d) Why iron corrosion is a serious problem: Iron is the most widely used structural metal in bridges, ships, railway tracks, automobiles, and buildings. Rusting continuously eats away and structurally weakens these iron objects, leading to catastrophic structural failures and costing billions of dollars annually in damage and replacement.

(e) Prevention of corrosion: Corrosion can be prevented by isolating the metal surface from air and moisture using the following methods:

1. Painting, oiling, or greasing the surface.
2. Galvanisation (coating iron or steel with a thin protective layer of zinc).
3. Anodising (forming a thick, protective oxide layer on metals like aluminium).
4. Alloying (mixing the metal with other metals or non-metals to change its properties).