Answer:
Cooking an egg
Step-by-step explanation:
Molecular composition is altered when an egg is cooked. Old chemical bonds are broken and new ones are made. Here, the globular proteins found in egg are denatured due to the bonds being broken. These denatured proteins from an entangled structure and it can not be brought back into its original structure. Hence, molecular composition of the egg is altered.
In the rest of the three options the change is physical and molecular composition stays the same.