Which of the following is a reliable indicator that a chemical change has occurred?

• A. Change in the physical state, such as melting or boiling
• B. Dissolving a solid in a liquid
• C. Formation of a new substance with different properties
• D. Change in size or shape of the material

Answer: (C)

Verified step by step guidance

1. Understand the difference between physical and chemical changes. A physical change affects the form of a substance but not its chemical composition, while a chemical change results in the formation of one or more new substances with different properties.
2. Analyze each option to determine if it represents a physical or chemical change. For example, melting or boiling involves a change in physical state but the substance remains the same chemically.
3. Recognize that dissolving a solid in a liquid is a physical change because the solid's chemical identity does not change; it is simply dispersed in the liquid.
4. Note that a change in size or shape is a physical change since it only alters the appearance or form of the material without changing its chemical structure.
5. Identify that the formation of a new substance with different properties is the key indicator of a chemical change, as it signifies that a chemical reaction has occurred producing new substances.