Question

When air is blown from mouth into a test-tube containing lime water, the lime water turns milky due to the presence of ______.

Options

• oxygen

• carbon dioxide

• nitrogen

• water vapour

Answer 1

When air is blown from mouth into a test-tube containing lime water, the lime water turns milky due to the presence of carbon dioxide.

Explanation:

When we blow air into lime water, the carbon dioxide (CO₂) present in exhaled air reacts with lime water (calcium hydroxide) to form calcium carbonate, which makes the lime water turn milky.

\[\ce{Ca(OH)2 + CO2 -> CaCO3 + H2O}\]