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Science (086) — AI-generated practice question

AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.

Q1. [1] medium exam-ready
When carbon dioxide gas is passed in excess through lime water, the white precipitate of calcium carbonate: (A) Remains unchanged (B) Turns yellow (C) Dissolves to form a soluble compound (D) Changes to calcium oxide
  1. A Remains unchanged
  2. B Turns yellow
  3. C Dissolves to form a soluble compound
  4. D Changes to calcium oxide
Generated by claude-sonnet-4-6 · 2026-06-26 01:03 · grounding rag
Model Answer

(C) Dissolves to form a soluble compound

When excess CO₂ is passed through lime water, CaCO₃ reacts with CO₂ and water to form calcium bicarbonate [Ca(HCO₃)₂], which is soluble, so the white precipitate dissolves.

Explanation

The key reaction is: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂. Calcium bicarbonate is soluble in water, so the milky/white precipitate disappears when CO₂ is in excess. This is a standard two-step lime water test concept tested in board exams. Remember: limited CO₂ → milky (CaCO₃ precipitate); excess CO₂ → clear solution (Ca(HCO₃)₂).

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