The gas evolved in the diagrammatic set up given below turns calcium hydroxide solution milky. The gas evolved is:

CO₂

Reason — The setup shows ethanoic acid reacting with sodium carbonate. This reaction produces carbon dioxide gas, which when passed through calcium hydroxide solution [lime water] turns it milky due to the formation of insoluble calcium carbonate:

$$\begin{aligned}\text{2CH₃COOH} + \text{Na₂CO₃} \rightarrow 2\text{CH₃COONa} + \text{H₂O} + \text{CO₂} \uparrow \\[1em] \text{CO₂} + \text{Ca(OH)₂} \rightarrow \text{CaCO₃} \downarrow + \text{H₂O}\end{aligned}$$

Hence, the gas evolved is carbon dioxide (CO₂).