**Chemical Change: Rusting of Iron**

Chemical changes involve the formation of new substances with different properties from the original substances. In the given options, the only process that represents a chemical change is the rusting of iron.

**Rusting of Iron:**

Rusting is a chemical process that occurs when iron reacts with oxygen and water in the presence of certain impurities. It is a slow oxidation process that results in the formation of a reddish-brown compound called iron(III) oxide, commonly known as rust.

**Explanation:**

The rusting of iron involves the following steps:

1. **Formation of Iron Oxide:** When iron is exposed to oxygen in the presence of water, it undergoes oxidation to form iron(II) ions (Fe²⁺). This reaction can be represented as:

4Fe(s) + 3O₂(g) + 6H₂O(l) → 4Fe²⁺(aq) + 12OH⁻(aq)

The iron(II) ions further react with oxygen and water to form iron(III) ions (Fe³⁺) and hydroxide ions (OH⁻):

4Fe²⁺(aq) + O₂(g) + 4H₂O(l) → 4Fe³⁺(aq) + 8OH⁻(aq)

2. **Formation of Rust:** The iron(III) ions react with hydroxide ions to form iron(III) hydroxide (Fe(OH)₃). This compound is not stable and undergoes dehydration to form iron(III) oxide (Fe₂O₃), which is commonly known as rust:

2Fe³⁺(aq) + 6OH⁻(aq) → Fe₂O₃(s) + 3H₂O(l)

Rust is a hydrated form of iron(III) oxide, and its chemical formula is often written as Fe₂O₃·xH₂O.

3. **Characteristics of Rust:** Rust is a brittle, porous material that weakens the iron structure. It has a reddish-brown color and flakes off easily. Rusting is an electrochemical process that occurs more rapidly in the presence of moisture and salt, as these substances facilitate the flow of electrons and ions.

**Conclusion:**

Among the given options, the rusting of iron is the only process that involves a chemical change. Dissolving of common salt into water is a physical change, as it does not result in the formation of new substances. Changing of water into ice and melting of ice are also physical changes, as they involve a change in the state of matter without any chemical reactions.