Which of the following is an indicator that a chemical reaction has occurred?

• A. Dissolving of sugar in water
• B. Formation of a gas
• C. Melting of ice
• D. Change in physical state without new substance formation

Answer: (B)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different chemical properties, whereas physical changes do not produce new substances.
2. Analyze each option to determine if it represents a chemical or physical change:
3. - Dissolving sugar in water is a physical change because sugar molecules disperse but do not chemically change.
4. - Formation of a gas often indicates a chemical reaction because new gaseous products are formed from reactants.
5. - Melting of ice and changes in physical state involve phase changes, which are physical changes without new substances being formed.