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

• A. Formation of a gas or bubbles
• B. Change in the shape of a substance
• C. Breaking a glass into pieces
• D. Melting of ice into water

Answer: (A)

Verified step by step guidance

1. Understand that a chemical change involves the formation of new substances with different properties, while a physical change affects only the form or state of a substance without changing its identity.
2. Identify the options that indicate a chemical change by looking for signs such as color change, temperature change, formation of a precipitate, or formation of a gas (bubbles).
3. Recognize that 'Formation of a gas or bubbles' is a classic indicator of a chemical reaction because it shows that a new substance (gas) is being produced.
4. Note that 'Change in the shape of a substance', 'Breaking a glass into pieces', and 'Melting of ice into water' are physical changes because they do not produce new substances; they only change the form or state.
5. Conclude that the correct sign of a chemical change among the options is the 'Formation of a gas or bubbles' because it reflects a chemical transformation.