AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(C) Change in shape
According to the textbook, the indicators of a chemical reaction are change in state, change in colour, evolution of a gas, and change in temperature — not change in shape.
Source: Chapter 1, Chemical Reactions and Equations (Activity 1.1–1.3 observations)
The textbook explicitly lists four observations that indicate a chemical reaction: change in state, change in colour, evolution of a gas, and change in temperature. "Change in shape" is a physical change (e.g., cutting, bending) and does NOT indicate a new substance has formed. Examiners expect students to recall this list precisely — note it is "change in state," not "change in shape."