Carbon Dioxide Detection in Air Using Limewater

Steps:

• Atmospheric air contains a small amount of CO2, which reacts with limewater (calcium hydroxide) to form insoluble calcium carbonate, turning it cloudy.
• Air is pumped into test tube 1, exposing limewater directly to incoming air, causing cloudiness.
• The air then passes through an absorber (like soda lime) that removes CO2 before reaching test tube 2.
• After 10 minutes, tube 1 shows cloudiness from CO2 reaction, while tube 2 remains clear due to CO2 absence.

Why B is correct:

• Limewater turns cloudy specifically with CO2 (Ca(OH)2 + CO2 → CaCO3 + H2O), confirming atmospheric CO2 in tube 1 but not in tube 2 post-absorption.

Why the others are wrong:

• A: Ignores CO2 in air, so tube 1 should cloud.
• C: Assumes no absorption, but tube 2 lacks CO2 after filtering.
• D: Reverses the setup; tube 1 gets unfiltered air first.

Final answer: B