Look at the figure and answer the following questions:
$(a)$ What change would you observe in the calcium hydroxide solution taken in tube $B$?
$(b)$ Write the chemical reactions involved in test tubes $A$ and $B$ respectively.

(N/A) The calcium hydroxide solution will turn milky due to the formation of calcium carbonate.
$(b)$ The chemical reactions are as follows:
In test tube $A$: Ethanoic acid reacts with sodium carbonate to produce carbon dioxide gas.
$2CH_{3}COOH + Na_{2}CO_{3} \rightarrow 2CH_{3}COONa + H_{2}O + CO_{2}$
In test tube $B$: Carbon dioxide gas reacts with calcium hydroxide (lime water) to form calcium carbonate,which makes the solution milky.
$Ca(OH)_{2} + CO_{2} \rightarrow CaCO_{3} + H_{2}O$
Note: If excess $CO_{2}$ is passed through the solution,the milkiness disappears due to the formation of soluble calcium bicarbonate.
$CaCO_{3} + H_{2}O + CO_{2} \rightarrow Ca(HCO_{3})_{2}$