Science — AI-generated practice question

When excess CO₂ is passed through milky lime water, the white precipitate (calcium carbonate) dissolves and the solution turns clear/colourless. This happens because excess CO₂ reacts with CaCO₃ and water to form calcium bicarbonate, which is soluble in water:

$$\text{CaCO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \rightarrow \text{Ca(HCO}_3)_2(aq)$$

Source: Chapter 1, Section 1.2.1 (Combination Reaction)

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• The examiner expects two things: the observation (turns clear) and the reason (CaCO₃ converts to soluble Ca(HCO₃)₂).
• Writing the balanced equation earns a mark and shows understanding.
• This is a classic two-step lime water reaction frequently asked in CBSE exams — milky due to CaCO₃ formation, then clear due to Ca(HCO₃)₂ formation on excess CO₂.