Question

The most durable metal plating on iron to protect against corrosion is:
(A) Tin plating
(B) Zinc plating
(C) Copper plating
(D) Nickel plating

Answer 1

Hint: Iron when exposed to atmosphere reacts with the oxygen present and hence gets oxidized, this is how iron corrodes. This is the reason to add a coating of another metal to prevent iron from corroding. However, the metal must be resistant to corrosion in order to serve the purpose.

Complete step by step answer:
Galvanization is the process of applying a protective zinc coating to iron, to stop corrosion.
The most common method is hot-dip galvanizing, during which the parts are submerged during a bath of molten hot zinc.
Galvanizing protects the underlying iron or steel in the following main ways:
-The zinc coating, when intact, prevents corrosive substances from reaching the underlying steel or iron.
-The zinc protects iron by corroding first. For better and long-term results, chromates along with zinc are used to galvanize iron.
-In the event the underlying metal becomes exposed, protection can continue as long as there is zinc close enough to be coupled electrically. Once the zinc in the area is consumed local corrosion of the base metal starts.
Hence from the above explanation, we can conclude that zinc metal is used for galvanization as it prevents the corrosion of base metal (mainly iron) as zinc does not react with the oxygen present in the atmosphere and hence does not corrode.

Therefore, the correct answer is option (B).

Note: Although galvanizing will prevent the attack of the base metal ( here, iron), corrosion is an inevitable phenomenon. After years of exposure, the metal will eventually start to corrode. For example, corrugated iron sheets used in roofs will start rusting in a few years. Galvanized iron exposed to the marine environment will start rusting as the zinc metal is converted to soluble zinc chloride which simply washes away.