Q1. [1] medium thorough-understanding
Assertion (A): When excess carbon dioxide is bubbled through lime water that has already turned milky, the white precipitate dissolves and the solution becomes clear again.
Reason (R): Calcium carbonate reacts with water and carbon dioxide to form calcium hydrogencarbonate, which is soluble in water.
Choose the correct option:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true but R is false.
(D) A is false but R is true.
- A Both A and R are true, and R is the correct explanation of A.
- B Both A and R are true, but R is NOT the correct explanation of A.
- C A is true but R is false.
- D A is false but R is true.
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
(A) Both A and R are true, and R is the correct explanation of A.
When excess CO₂ is passed through milky lime water, CaCO₃ reacts with H₂O and CO₂ to form Ca(HCO₃)₂ (calcium hydrogencarbonate), which is soluble, making the solution clear again. R correctly explains A.
Explanation
The key chemistry here: CO₂ + H₂O + CaCO₃ → Ca(HCO₃)₂. Both statements are factually correct, and R directly explains the mechanism behind A — the dissolving of the white precipitate is caused by formation of soluble calcium hydrogencarbonate. This is a standard "excess CO₂ with lime water" observation tested in CBSE boards. Option A is correct.