Which of the following statements regarding rusting of iron are true? (a) It…

Corrosion (of which rusting is the iron-specific case) is a chemical process in which a metal reacts with substances in its environment — typically oxygen and moisture — to form a new compound at its surface. Such oxidation reactions are generally exothermic (they release energy), and once the reactants (metal, oxygen, moisture) are present, they need no external heat to start — they proceed spontaneously at ordinary room temperature. Once the new compound (the oxide) has formed, though, it does not spontaneously decompose back into the original metal and oxygen — corrosion reactions are not reversible under normal conditions.

Rusting fits this pattern exactly: iron reacts with oxygen in the presence of moisture through a genuine chemical change (forming hydrated iron oxide, commonly called rust) rather than a physical change; the process releases heat as it proceeds; and it needs no special heating to begin — ordinary atmospheric conditions are sufficient.

What does not fit is the idea that this process runs in reverse on its own: once the oxide layer has formed, it does not spontaneously decompose back into metallic iron and oxygen under normal conditions — reversing it requires a deliberate reduction process, which plays no part in natural rusting.

So the option reflecting rusting's chemical, energetic, and thermal character — without assuming it reverses naturally — is the one that correctly describes the process.