Which of the following determines that a chemical reaction has not taken place?

Correct option is B

Correct Answer: (B) Change in size

Explanation:
A change in size does not necessarily indicate that a chemical reaction has taken place. A chemical reaction typically involves the formation of new substances with different properties from the original ones. While a change in size might occur in physical processes (such as cutting or breaking a substance), it does not necessarily involve a chemical change.

Other Options:

• Change in state: A change in state (e.g., solid to liquid, liquid to gas) could indicate a physical change, but it is not conclusive evidence of a chemical reaction by itself.
• Change in colour: A change in colour is often a sign of a chemical reaction, especially when new substances are formed (e.g., rusting of iron).
• Evolution of a gas: The production of a gas is a clear indicator that a chemical reaction has taken place, as new chemical substances are formed.