As the melting of wax can be turned bask to a solid form of wax as compared to other options like rusting of iron and all!

Rusting of iron:
Rusting of iron is a chemical change. It occurs when iron reacts with oxygen and moisture in the air to form iron oxide (rust). This process involves a chemical reaction that changes the composition and properties of the iron.

Combustion of magnesium ribbon:
The combustion of magnesium ribbon is also a chemical change. It involves the reaction of magnesium with oxygen in the air to produce magnesium oxide. This chemical reaction results in the formation of a new substance with different properties.

Burning of candle:
The burning of a candle is a chemical change. When a candle burns, the wax (which is a hydrocarbon) reacts with oxygen in the air to produce carbon dioxide, water vapor, and heat. This chemical reaction is known as combustion.

Melting of wax:
The melting of wax is a physical change. It involves the change of state from a solid to a liquid without any change in the chemical composition of the wax. The wax molecules are still the same, but their arrangement changes as they gain enough energy to overcome the forces holding them together in a solid state.

Explanation:
A physical change is a change that only affects the physical properties of a substance, such as its shape, size, or state of matter, without changing its chemical composition. In the case of the melting of wax, the wax undergoes a physical change from a solid to a liquid, but the chemical composition of the wax remains the same.

On the other hand, rusting of iron, combustion of magnesium ribbon, and burning of a candle are all examples of chemical changes. These processes involve chemical reactions that result in the formation of new substances with different properties.

Therefore, the correct answer is option D, melting of wax, as it is the only example that represents a physical change.