What is $Calgon$,used as a water softener?

Which can be used to prepare pure and demineralised $H_2O$ ?

When temporary hard water containing $Mg(HCO_3)_2$ is boiled,the precipitate formed is of:

Match the reactants in List-$I$ with the products in List-$II$.

List-$I$	List-$II$
$(a). H_2O + H_2S$	$(i). (H_3O^{+}, HS^{-})$
$(b). H_2O + N^{3-}$	$(ii). (NH_3, OH^{-})$
$(c). H_2O + SiCl_4$	$(iii). (OH^{-}, H_3S^{+})$
$(d). H_2O + F_2$	$(iv). (SiO_2, HCl)$
	$(v). (SiO_4^{4-}, Cl_2)$
	$(vi). (O_2, F^{-})$
	$(vii). (HF, OH^{-})$
	$(viii). (OH^{-}, NH_3)$

Given below are two statements:
Statement-$I$: Permutit process is more efficient compared to the synthetic resin method for the softening of water.
Statement-$II$: Synthetic resin method results in the formation of soluble sodium salts.
In the light of the above statements,choose the most appropriate answer from the options given below:

When a molten ionic hydride is electrolysed: