Question

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

• A. oxygen
• B. carbon dioxide
• C. nitrogen
• D. water vapour

Answer 1

The correct option is B

carbon dioxide

The correct option is B

Explanation of the correct option:

1. Respiration is the process by which a cell uses glucose.
2. It occurs in the presence of oxygen.
3. Respiration produces ATP and carbon dioxide as a byproduct.
4. Carbon dioxide is released during the exhalation of air from the lungs.
5. The partial pressure of carbon dioxide gas in exhaled air is high.
6. When exhaled air is blown into a test tube containing lime water, it is converted into limestone.
7. Limewater becomes milky in the presence of carbon dioxide.
8. Reaction involved: $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{CO}}_2\left(\mathrm{aq}\right)\to {\mathrm{CaCO}}_3\left(\mathrm{s}\right)\downarrow +{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Final answer: When air is blown from the mouth into a test tube containing lime water, the lime water turned milky due to the presence of carbon dioxide.