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The observation of bubbling or effervescence during a reaction indicates:
A{'text': 'A precipitate is forming'}
B{'text': 'A gas is being evolved'}
C{'text': 'A coloured solid is settling'}
D{'text': 'No reaction is occurring'}
Answer & Solution
Correct answer: B. {'text': 'A gas is being evolved'}
1. Effervescence is the rapid escape of bubbles from a liquid.
2. Bubbles are formed because a **gas is being produced** during the chemical change.
3. Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑.
4. A precipitate is a solid (not a gas) and absence of bubbling does not mean no reaction.
_Source: Selina Concise ICSE Class 8 Chemistry Ch 6 "Chemical Reactions", Signs of chemical change_
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