Which of the following statements correctly compares physical and chemical properties?

• A. Physical properties always involve a change in the chemical composition of a substance.
• B. Physical properties and chemical properties both require a chemical reaction to be observed.
• C. Physical properties can be observed without changing the substance's chemical identity, while chemical properties describe the ability of a substance to undergo chemical changes.
• D. Chemical properties can be measured without altering the substance's identity.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the definitions of physical and chemical properties. Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity, such as color, melting point, or density.
2. Step 2: Recognize that chemical properties describe a substance's ability to undergo chemical changes, meaning the substance's chemical composition changes during the observation, such as flammability or reactivity with acids.
3. Step 3: Analyze the first statement: 'Physical properties always involve a change in the chemical composition of a substance.' This is incorrect because physical properties do not require a chemical change.
4. Step 4: Analyze the second statement: 'Physical properties and chemical properties both require a chemical reaction to be observed.' This is incorrect because physical properties can be observed without any chemical reaction.
5. Step 5: Evaluate the correct statement: 'Physical properties can be observed without changing the substance's chemical identity, while chemical properties describe the ability of a substance to undergo chemical changes.' This accurately distinguishes the two types of properties.