Chemical Change:
A chemical change refers to a process in which one or more substances are transformed into different substances with new properties. This change occurs at a molecular level and involves the breaking and forming of chemical bonds.

Melting of wax:
The melting of wax is a physical change rather than a chemical change. It involves the phase transition of wax from a solid state to a liquid state. The process of melting does not alter the chemical composition of the wax, only its physical state.

Mixing of iron filings with sulfur powder:
The mixing of iron filings with sulfur powder is a physical change. It involves the combination of two substances to form a mixture. The iron filings and sulfur powder can be easily separated by physical means such as using a magnet to attract the iron filings or filtering to separate the components. The chemical properties of iron and sulfur remain unchanged in this process.

Cooking of food:
The cooking of food involves various chemical changes. When food is cooked, it undergoes a series of chemical reactions that result in changes in taste, texture, and nutritional value. These changes occur due to the application of heat and the interaction of heat with the food's components, such as proteins, carbohydrates, and fats. For example, proteins denature and coagulate, starches gelatinize, and sugars caramelize during the cooking process. These chemical changes are irreversible and result in the transformation of the raw ingredients into a cooked dish.

Dissolving salt in water:
The dissolving of salt in water is a physical change. It involves the separation of sodium and chloride ions from the crystal lattice of salt and their dispersion in water. The resulting solution is a homogeneous mixture of salt and water. Although the physical appearance of the salt may change, the chemical composition of the salt remains the same. The salt can be recovered by evaporating the water, indicating that no chemical change has occurred.

In conclusion, out of the given options, the cooking of food is the only process that involves chemical changes. The melting of wax, mixing of iron filings with sulfur powder, and dissolving salt in water are all physical changes.

Not phisical change