Final answer:
The observation that indicates a chemical property from the given options is 'ignites in water,' as it relates to the material's reactivity, which is indicative of its ability to undergo a chemical reaction.
Step-by-step explanation:
An observation of a chemical property involves a characteristic that can be observed during a chemical reaction, where the substance's chemical identity is changed. From the options provided, the one that is an observation of a chemical property is 'ignites in water.' This is because ignition upon contact with water is indicative of a material's reactivity, which is a characteristic related to how a substance engages in chemical reactions. Other examples of chemical properties include flammability, the ability to corrode, and reactivity with other chemicals.
Regarding the educational exercises:
- Exercise 3.5.1B and 1.4.1B identify flammability as a chemical property.
- In Exercise 7.2.2, corroding metal and fireworks exploding are examples of chemical reactions, implicating a chemical property or change.