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Science (086) — CBSE Class 10 board question

Q1. [2] § Chapter Introduction
A student performs the following experiment in his school laboratory. List two observations to justify that in this experiment a chemical change has taken place.
Previously asked in CBSE board exam
2025 31/1/1 Q21
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Generated by claude-sonnet-4-6 · 2026-06-14 10:31 · grounding rag
Model Answer

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

Explanation

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.

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Previous-year CBSE Grade 10 board exam questions, organised by subject and chapter, each with a model answer — free to read and print.