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Which sequence correctly lists three indicators of a chemical change that occur together in Zn + H₂SO₄?
A{'text': 'Gas evolution, rise in temperature, no colour change'}
B{'text': 'Gas evolution, no temperature change, colour change'}
C{'text': 'Precipitate, no gas, fall in temperature'}
D{'text': 'Colour change, precipitate, no gas evolution'}
Answer & Solution
Correct answer: A. {'text': 'Gas evolution, rise in temperature, no colour change'}
1. Zn reacts with H₂SO₄ to give ZnSO₄ and H₂.
2. Visible signs: hydrogen gas bubbles out → **gas evolution**.
3. The reaction is exothermic, so the test tube becomes hot → **rise in temperature**.
4. Both Zn (grey solid) and the solution stay colourless → **no colour change**.
5. Hence the matching set is gas evolution + rise in temperature + no colour change.
_Source: Selina Concise ICSE Class 8 Chemistry Ch 6 "Chemical Reactions", Signs of chemical change_
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