Explanation:
Washing soda, \(\left(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}\right)\) is used to remove permanent hardness of water. It converts \(\mathrm{Ca}^{2+}\) and \(\mathrm{Mg}^{2+}\) salts (soluble) to carbonates (insoluble).
\[\begin{array}{l}
{\rm{MgC}}{{\rm{l}}_{\rm{2}}} + {\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}} \to {\rm{MgC}}{{\rm{O}}_{\rm{3}}} \downarrow \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, + {\rm{2NaCl}}
\end{array}\]
\[\begin{array}{l}
{\rm{CaS}}{{\rm{O}}_{\rm{4}}} + {\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{C}}{{\rm{O}}_{\rm{3}}} \to {\rm{CaC}}{{\rm{O}}_{\rm{3}}} \downarrow \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, + {\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}
\end{array}\]
