Which of the following correctly lists signs of a chemical change and provides an example of a physical change?

• A. Signs: color change, formation of a precipitate; physical change example: melting ice
• B. Signs: boiling point changes; physical change: tearing paper
• C. Signs: melting; physical change: rusting
• D. Signs: color change; physical change: evaporating liquid

Answer: (A)

Recognizing a chemical change means looking for indicators that new substances are formed. Color change and the formation of a precipitate are classic signs because they show a chemical reaction has produced substances different from the originals. Melting ice is a physical change, since it only changes the state of water from solid to liquid without changing its chemical identity. This pairing—recognizing a chemical-change sign and giving a physical-change example—clearly separates the idea of changing composition from simply changing form. The other options mix signs that aren’t definitive indicators of a chemical reaction or pair a physical change with a sign that could occur in nonreactive processes, such as mixing in indicators like boiling point changes (a property change), tearing paper (physical), melting (physical), or pairing color change with evaporating liquid (which can occur without chemical change).