Which process is an example of a chemical change?

Cooking an egg is an example of a chemical change because it involves a transformation that alters the molecular structure of the proteins in the egg. When an egg is cooked, heat causes these proteins to denature and coagulate, resulting in a change from a liquid to a solid state. This process is irreversible; once the egg is cooked, it cannot go back to its original state.

In contrast, melting ice, dissolving sugar in water, and subliming dry ice are physical changes. Melting ice changes the state of water from solid to liquid, but the chemical composition of H₂O remains the same. Similarly, dissolving sugar in water mixes the two substances physically, but the sugar retains its chemical identity in solution. Subliming dry ice, which transitions from solid to gas, also does not alter the chemical structure of carbon dioxide. Therefore, cooking an egg is the only option that demonstrates a chemical change.