Which of the following is an example of a chemical reaction indicator that may be observed during a chemical change?

• A. Change in temperature without any reaction
• B. Melting of ice
• C. Formation of a gas
• D. Dissolving sugar in water

Answer: (C)

Verified step by step guidance

1. Understand that a chemical reaction indicator is a sign that a chemical change has occurred, which means the substances involved have transformed into new substances with different properties.
2. Review each option to determine if it represents a chemical change or a physical change. Physical changes do not produce new substances, while chemical changes do.
3. Recognize that 'Change in temperature without any reaction' is not an indicator of a chemical reaction because no new substances are formed; it could be a physical process.
4. Identify that 'Melting of ice' and 'Dissolving sugar in water' are physical changes because the substances retain their original chemical identities despite the change in state or mixing.
5. Note that 'Formation of a gas' is a common indicator of a chemical reaction because it shows that new substances are being produced, often visible as bubbles or fizzing.