In corrosion:
A. A metal is oxidized by loss of electrons to oxygen.
B. It is an electrochemical phenomenon
C. The object under corrosion behaves as anode.
D. Coating the metal with \(Zn\) can save iron object from corrosion.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, B, C, D only
Corrosion of iron is an electrochemical process: at one spot of the object iron is oxidised (that spot is the anode), and at another spot oxygen is reduced, the electrons flowing through the metal.
(A) A metal is oxidized by loss of electrons to oxygen. — True. Iron loses electrons, and these electrons reduce \( \ce{O2} \).
(B) It is an electrochemical phenomenon — True. Oxidation at one spot and reduction at another, with electrons moving through the metal, make a tiny electrochemical cell.
(C) The object under corrosion behaves as anode. — True. The spot where iron is oxidised acts as the anode:
\( \displaystyle \text{Anode: }\ce{2Fe(s) -> 2Fe^2+ + 4e^-} \)
\( \displaystyle \text{Cathode: }\ce{O2(g) + 4H+(aq) + 4e^- -> 2H2O(l)} \)
\( \displaystyle \text{Cell: }\ce{2Fe(s) + O2(g) + 4H+(aq) -> 2Fe^2+(aq) + 2H2O(l)}\qquad E^\circ_{\text{cell}} = 1.67\ \mathrm{V} \)
(D) Coating the metal with Zn can save iron object from corrosion. — True. Zinc covers the surface, and being more reactive it corrodes itself in preference to iron (sacrificial protection, galvanisation).
NCERT (2026-27 edition):
Corrosion – “In corrosion, a metal is oxidised by loss of electrons to oxygen and formation of oxides. Corrosion of iron (commonly known as rusting) occurs in presence of water and air. The chemistry of corrosion is quite complex but it may be considered essentially as an electrochemical phenomenon. At a particular spot (Fig. 2.13) of an object made of iron, oxidation takes place and that spot behaves as anode and we can write the reaction
Anode: 2Fe(s) → 2Fe2+ + 4e− E°(Fe2+/Fe) = –0.44 V”
Corrosion – “… Prevention of corrosion is of prime importance. It not only saves money but also helps in preventing accidents such as a bridge collapse or failure of a key component due to corrosion. One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere. This can be done by covering the surface with paint or by some chemicals (e.g. bisphenol). Another simple method is to cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object. An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object.”