The reagent(s) used for softening the temporary hardness of water...

Softening the temporary hardness of water means conversion of bicarbonate into calcium carbonate (precipitation) \begin{gathered}\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_2+ \mathrm{Ca}(\mathrm{OH})_2 \longrightarrow \\ 2 \mathrm{CaCO}_{3} \downarrow+2 \mathrm{H}_{2} \mathrm{O}\\ \mathrm{Ca}\left(\mathrm{HCO} }_{3}\right)_2+\mathrm{Na}_{2} \mathrm{CO}_{3} \longrightarrow \\ \mathrm{CaCO}_{3} \downarrow+2 \mathrm{NaHCO} }_{3} \end{gathered} Even \mathrm{NaOCl} can be used, as in aqueous medium $\overline{\mathrm{O}} \mathrm{Cl}$ gets hydrolysed and makes solution alkaline enough to cause precipitation of $\mathrm{CaCO}_3 .$\begin{aligned}\mathrm{NaOCl}+\mathrm{H}_{2} \mathrm{O}& \rightleftharpoons \mathrm{HOCl}+\mathrm{NaOH}\\ \mathrm{OH}^{-}+\mathrm{HCO} }_{3}^{-} & \longrightarrow \mathrm{CO}_{3}^{2-}+ \mathrm{H}_{2} \mathrm{O} \end{aligned}$$ Representative elements (Hydrogen and its compounds) Conceptual II