Final answer:
Among the given options, water boiling and becoming a gas is a physical change since it involves a change of state without altering the chemical composition of the substance.
Step-by-step explanation:
Among the given options, water boiling and becoming a gas is an example of a physical change. When water boils, it changes from its liquid state (water) to gas (steam), but it remains H₂O throughout the process, meaning that no chemical bonds are broken or formed during this transformation.
An iron nail rusting, on the other hand, is an example of a chemical change. Rusting occurs when iron reacts with oxygen in the air to form iron oxide (rust), which is a different substance with different properties. The fact that the nail changes color and composition is evidence of this chemical change.
Vinegar reacting with baking soda, and leaves changing colors in the fall, are also chemical changes, but they are not the correct answer to the given question. So to summarize, the bubbling of vinegar and baking soda, and the leaves changing color are not examples of a physical change, but water boiling is.