Corrosion of iron is which type of phenomenon?

Electrochemical phenomenon

The correct answer is option 2. Electrochemical phenomenon.

Corrosion of iron occurs due to an electrochemical process involving oxidation and reduction reactions. Here's an explanation of why it is considered an electrochemical phenomenon:

Oxidation of Iron: Iron \((Fe)\) metal reacts with oxygen \((O_2)\) from the atmosphere in the presence of moisture (water) to form iron oxide (rust). The reaction can be represented as:

\(\text{Fe} \rightarrow \text{Fe}^{2+} + 2e^-\)

This oxidation reaction releases electrons.

Reduction Reactions: The released electrons are then consumed in reduction reactions, typically involving oxygen and water:

\(\text{Oxygen Reduction Reaction: } \frac{1}{2}\text{O}_2 + \text{H}_2\text{O} + 2e^- \rightarrow 2\text{OH}^- \)

\(\text{Water Reduction Reaction: } 2\text{H}_2\text{O} + 2e^- \rightarrow \text{H}_2 + 2\text{OH}^- \)

These reduction reactions occur either directly at the metal surface or in the electrolyte (moisture) surrounding the iron.

Electrochemical Cell Formation: The process involves the formation of localized electrochemical cells on the iron surface where different areas act as anodes (where oxidation occurs) and cathodes (where reduction occurs). This leads to the flow of electrons (electric current) through the metal.

Rust Formation: The iron ions \((Fe^{2+})\) generated from the oxidation combine with hydroxide ions \((OH^-)\) to form iron hydroxides, which then dehydrate and oxidize further to form various iron oxides (rust). Rust is porous and can allow further penetration of oxygen and water, accelerating the corrosion process.

Electrolytic Phenomenon: The presence of moisture (electrolyte) facilitates the movement of ions and electrons necessary for the oxidation and reduction reactions. This electrolytic environment enhances the corrosion process.

In summary, corrosion of iron involves complex electrochemical reactions where iron metal is oxidized and forms iron oxides due to the presence of oxygen and moisture. This classification as an electrochemical phenomenon highlights the role of oxidation-reduction reactions and the formation of electrochemical cells in the corrosion process.