RRB NTPC Prelims Model Paper 5 with solutions

(1) Lime water turns milky due to reaction of CaO with$\mathit{C}{\mathit{O}}_2$ forming $\mathit{C}\mathit{a}\mathit{C}{\mathit{O}}_{3.}\mathit{C}\mathit{a}\mathit{C}{\mathit{O}}_3$is insoluble in lime water and precipitates. But this milkiness disappears after we pass excess of$\mathit{C}{\mathit{O}}_2$ since calcium hydrogen carbonate$\left[\mathit{C}\mathit{a}{\left(\mathit{H}\mathit{C}{\mathit{O}}_3\right)}_2\right]$ is formed which is soluble in lime water.