Which of the following is NOT a sign that a chemical reaction has occurred?

• A. Change in state from solid to liquid due to melting
• B. Production of a gas
• C. Formation of a precipitate
• D. Change in color

Answer: (A)

Verified step by step guidance

1. Understand that a chemical reaction involves the breaking and forming of chemical bonds, resulting in new substances with different properties.
2. Identify common signs of a chemical reaction, such as production of a gas (bubbling or fizzing), formation of a precipitate (solid formed in a solution), and change in color (indicating new substances).
3. Recognize that a change in state, such as melting from solid to liquid, is a physical change, not a chemical change, because the substance's chemical identity remains the same.
4. Compare each option to determine which one does not indicate a chemical reaction; the change in state due to melting is a physical change and thus not a sign of a chemical reaction.
5. Conclude that the correct answer is the change in state from solid to liquid due to melting, as it does not involve the formation of new substances.