Freezing of water
Water freezing into ice is a physical change because it does not involve any change in the chemical composition of water molecules. It is simply a change in the physical state of water from liquid to solid. Let's break down this concept further:

Physical change:
- A physical change is a change in matter that does not result in the formation of a new substance.
- In the case of freezing water, the molecules rearrange themselves into a more ordered structure to form ice, but the chemical composition of water remains the same.

Process of freezing:
- When water is cooled below its freezing point (0 degrees Celsius or 32 degrees Fahrenheit), the kinetic energy of the water molecules decreases.
- As a result, the molecules slow down and come closer together, forming a crystalline structure characteristic of ice.
- This change in physical state is reversible, meaning that ice can be melted back into water by adding heat energy.

Comparison with other options:
- Rusting of iron (option a) involves a chemical reaction between iron and oxygen, resulting in the formation of a new substance (iron oxide).
- Baking a cake (option b) involves chemical reactions between ingredients like flour, sugar, and eggs, leading to the formation of a new substance (cake).
- Rotting of vegetables (option d) involves the decomposition of organic matter by microorganisms, resulting in the formation of new compounds.
In conclusion, the freezing of water is a physical change because it only involves a change in the physical state of water molecules without altering their chemical composition.