Question

Chemically rust is:

• A. Hydrated ferrous oxide
• B. Hydrated ferric oxide
• C. Only ferric oxide
• D. None of these

Answer 1

The correct option is B

Hydrated ferric oxide

The explanation for the correct option:

Rust: Rust is chemically ferric oxide$\left({\mathrm{Fe}}_2{\mathrm{O}}_3\right)$ where the oxidation state of iron is +3. The formation of rust takes place when the iron object is left undisturbed in an open environment wherein the presence of moisture reacts with oxygen which is present in the environment.

Basically rusting is a corrosive property in which iron reacts with oxygen to form brown colour rust which is generally hydrated ferric oxide.

Corrosion is the process of deterioration of materials as a result of chemical, electrochemical, or other reactions.

The chemical equation is as follows:

$$\begin{gathered} 4\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)+{\mathrm{nH}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{nH}}_2\mathrm{O}\left(\mathrm{s}\right) \\ \mathrm{Rust} \end{gathered}$$

So, we can understand that the rust is only hydrated ferric oxide.

The explanation for the incorrect options:

Option (A):- Hydrated ferrous oxide is $\mathrm{FeO}.{\mathrm{xH}}_2\mathrm{O}$ it does not form during rusting because in rusting the substances are in an open environment where they get a sufficient supply of oxygen and form ferric oxide as mentioned above.

Option (C):- Ferric oxide is the reaction of ferrous with oxygen only without the involvement of moisture formula is ${\mathrm{Fe}}_2{\mathrm{O}}_3$.

Hence, option (B) is the correct answer.