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

• A. Change in physical state from solid to liquid
• B. Breaking a glass into smaller pieces
• C. Dissolving sugar in water
• D. Formation of a gas

Answer: (D)

Verified step by step guidance

1. Understand that a chemical reaction involves the formation of new substances with different properties from the original substances.
2. Recognize that physical changes, such as changing from solid to liquid, breaking a glass, or dissolving sugar in water, do not produce new substances; they only change the form or state of the material.
3. Identify that evidence of a chemical reaction often includes indicators like formation of a gas, color change, temperature change, or formation of a precipitate.
4. Note that the formation of a gas during a process suggests that new substances are being produced, which is a hallmark of a chemical reaction.
5. Conclude that among the options given, the formation of a gas is the clear evidence that a chemical reaction has occurred.