Which of the following is NOT a sign of a chemical reaction?

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

Answer: (D)

Verified step by step guidance

1. Understand that a chemical reaction involves the rearrangement of atoms to form new substances, often accompanied by observable changes such as color change, gas production, or precipitate formation.
2. Recognize that a change in color can indicate a chemical reaction because it often reflects the formation of new substances with different properties.
3. Identify that the formation of a precipitate (a solid formed in a solution) is a clear sign of a chemical reaction, as it shows new compounds are being created.
4. Note that the production of a gas during a process is also a sign of a chemical reaction, indicating that new gaseous products are formed.
5. Understand that a change in state from solid to liquid due to melting is a physical change, not a chemical reaction, because it involves only a change in physical form without altering the chemical identity of the substance.