A physical change involves a change in the physical properties of a substance without altering its chemical composition. Let's analyze each option to determine which one represents a physical change:
- Rusting of iron - This is a chemical change where iron reacts with oxygen to form iron oxide (rust). The chemical composition of iron changes in this process.
- Burning of wood - This is a chemical change. Wood reacts with oxygen in the air to produce carbon dioxide, water, and other substances. The chemical composition of the wood changes during burning.
- Melting of ice - This is a physical change. Ice (solid water) changes to liquid water, but its chemical composition (H₂O) remains the same.
- Baking a cake - This is a chemical change. The ingredients (like flour, sugar, eggs) undergo chemical reactions when heated, resulting in new substances being formed.

Therefore, the correct answer is:
- Melting of ice