Which of the following is an example of an irreversible change?

• A. Melting ice
• B. Cooking an egg
• C. Mixing sand and water
• D. Boiling water

Answer: (B)

Cooking an egg is an example of an irreversible change because it involves a chemical transformation that alters the structure of the egg proteins. When an egg is cooked, the heat causes the proteins to denature and coagulate, resulting in a solid form that cannot return to its original raw state. This change is permanent; once the egg is cooked, it cannot be uncooked or transformed back to its initial condition.

In contrast, melting ice is a physical change that is reversible, as the ice can return to its solid state when cooled. Mixing sand and water also represents a reversible change, as you can separate the sand from the water through processes like filtration. Similarly, boiling water is a physical change where water changes from a liquid to a vapor, but it can be reversed by cooling the vapor back into liquid water.