Question

When air is blown from a mouth into a test tube containing lime water, the lime water turns 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

Explanation for the correct option:

(B) Carbon dioxide

• If air is blown into a test tube containing lime water, it turns milky due to the presence of carbon dioxide.
• The air blown out of the mouth contains Carbon dioxide (${\mathrm{CO}}_2$) that reacts with Calcium hydroxide ($\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$) (lime water) to form Calcium carbonate (${\mathrm{CaCO}}_3$) which appears milky.
• The reaction is as follows:

$\underset{\left(\mathrm{Calcium}\mathrm{hydroxide}\right)}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{l}\right)}+\underset{\left(\mathrm{Carbon}\mathrm{dioxide}\right)}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}\to \underset{\left(\mathrm{Calcium}\mathrm{carbonate}\right)}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Hence, option (B) is correct. The lime water turns milky due to the presence of Carbon dioxide.