How will you justify that rusting of iron is a chemical change?

Chemical change: A change in which one or more new substances are formed and their chemical properties get changed is known as chemical change. Most of the chemical changes are irreversible.

Rusting of iron:

• When iron is exposed to air and moisture, rusting takes place.
• Rust is nothing but Iron Oxide; a new product formed out of the reaction of iron with oxygen (exposure to air).

$\underset{\mathrm{Iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{2\mathrm{x}.{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Rust}}{2{\mathrm{Fe}}_2{\mathrm{O}}_3.{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{s}\right)}$

• Hence, rusting of iron is a chemical change as the reaction between iron and oxygen on exposure of air.