Science — CBSE Class 10 board question

Two observations that justify a chemical change has taken place:

1. Evolution of gas — Bubbles of gas are produced during the reaction (e.g., hydrogen gas is evolved when acid reacts with zinc granules).

1. Change in temperature — The test tube/conical flask becomes warm, indicating heat is released, showing a chemical change has occurred.

Source: Chapter 1, Chemical Reactions and Equations

The textbook (Activity 1.3) specifically lists four indicators of a chemical reaction: change in state, change in colour, evolution of a gas, and change in temperature. Since the figure likely shows acid + zinc (like Fig. 1.2), the two most relevant observations are gas evolution and temperature change. Pick any two valid indicators from the textbook list and briefly explain each — examiners award 1 mark per correct observation.