Which of the following is the best evidence that a chemical change has occurred?

• A. A substance is dissolved in water
• B. A change in the physical state, such as melting
• C. A change in size or shape
• D. A new substance with different properties is formed

Answer: (D)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes affect the form of a substance but not its chemical composition, while chemical changes result in the formation of new substances with different properties.
2. Analyze each option to determine if it indicates a physical or chemical change. For example, dissolving a substance in water or changing its physical state (like melting) are physical changes because the substance's chemical identity remains the same.
3. Recognize that a change in size or shape is a physical change since it only alters the appearance or form without changing the substance's chemical nature.
4. Identify that the formation of a new substance with different properties is the hallmark of a chemical change, as it indicates that the original substances have undergone a chemical reaction to produce something new.
5. Conclude that the best evidence for a chemical change is the formation of a new substance with different properties, distinguishing it clearly from physical changes.