Which of the following base is found in lime water?

Calcium hydroxide

The correct answer is option 1. Calcium hydroxide.

Lime water is a solution of calcium hydroxide (\( \text{Ca(OH)}_2 \)) in water. Calcium hydroxide is a white, crystalline solid that forms when calcium oxide (lime) reacts with water. The chemical equation for this reaction is:

\[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]

In the context of lime water, the solution contains the hydroxide ions (\( \text{OH}^- \)) derived from the dissociation of calcium hydroxide in water. The presence of hydroxide ions makes the solution basic (alkaline). Lime water is often used in various chemical tests, including the test for the presence of carbon dioxide, as it can react with carbon dioxide to form calcium carbonate, causing the solution to become cloudy. The chemical equation for this reaction is:

\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]

In summary, lime water contains calcium hydroxide as its base, and its alkaline properties are attributed to the hydroxide ions produced by the dissociation of calcium hydroxide in water.