Introduction:
Chemical changes involve the formation of new substances with different properties. They are characterized by the rearrangement of atoms and the breaking and forming of chemical bonds. In contrast, physical changes do not result in the formation of new substances and only affect the physical properties of a substance.

Explanation:
Among the given options, the boiling of water is a physical change and not a chemical change. Let's understand why boiling of water is a physical change and not a chemical change.

Physical Change:
Physical changes are those that affect the physical properties of a substance without changing its chemical composition. When water is boiled, it undergoes a physical change from a liquid to a gas. The water molecules gain enough energy to overcome the intermolecular forces holding them together, and they escape into the atmosphere as water vapor. The chemical composition of water (H2O) remains the same before and after boiling.

Chemical Change:
Chemical changes involve the formation of new substances with different chemical compositions and properties. Electrolysis of water, digestion of food, and burning of magnesium ribbon in oxygen are all examples of chemical changes.

- Electrolysis of water: Electrolysis of water involves the decomposition of water molecules into hydrogen gas (H2) and oxygen gas (O2) through the passage of an electric current. This results in the formation of new substances with different chemical compositions.
- Digestion of food: Digestion of food involves the breakdown of complex molecules into simpler molecules that can be absorbed by the body. Enzymes in the digestive system catalyze chemical reactions that result in the breakdown of food into nutrients.
- Burning of magnesium ribbon in oxygen to form magnesium oxide: When magnesium ribbon is burned in oxygen, it undergoes a chemical reaction to form magnesium oxide (MgO). The magnesium atoms combine with oxygen atoms to form a new substance with different properties.

Conclusion:
In conclusion, the boiling of water is a physical change because it only affects the physical properties of water without changing its chemical composition. The other options involve chemical changes where new substances are formed with different chemical compositions and properties.