Question

Assertion: Corrosion of iron is commonly known as rusting.

Reason: Corrosion of iron occurs in the presence of moist air.

• A. Both assertion and reason are false.
• B. Assertion is true, but the reason is false.
• C. Both assertion and reason are true. The reason is the correct explanation of assertion.
• D. Both assertion and reason are true. The reason is not the correct explanation of assertion.

Answer 1

The correct option is D

Both assertion and reason are true. The reason is not the correct explanation of assertion.

Explanation for assertion:-

• Rusting of iron is basically called corrosion.
• When the iron is exposed to moist air for a long time, it acquires a coating of a brown flaky substance which is called rust.
• Rust is hydrated Ferric oxide and has a chemical formula of ${\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}$
• Thus assertion is true.

Explanation for reason:-

• The moisture in the air is responsible for the rusting of iron.
• The water vapour and oxygen react with the surface of the iron and thus corrosion occurs.
• Oxygen is a good oxidising agent and Iron is a good reducing agent.
• Thus the iron readily gives up the electrons to the oxygen when it is left exposed.
• The complete reaction is:

$$\begin{gathered} \underset{\mathrm{Iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Ferric}\mathrm{oxide}}{2{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)} \\ \underset{\mathrm{Iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{water}}{{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{g}\right)}\to \underset{\mathrm{Hydrated}\mathrm{Ferric}\mathrm{oxide}}{{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{s}\right)\left(\mathrm{rust}\right)} \end{gathered}$$

• Thus reason is true but is not a correct explanation for assertion.

Therefore, (D) Both assertion and reason are true. The reason is not the correct explanation of assertion is the correct answer.