Which of the following ions are responsible for the hardness of water?

The degree of hardness of water is generally expressed in terms of which of the following?

Zeolite is hydrated sodium aluminium silicate. When treated with hard water,the sodium ions in zeolite are exchanged with

Some statements about heavy water are given below:
$(i)$ Heavy water is used as a moderator in nuclear reactors.
$(ii)$ Heavy water is more associated than ordinary water.
$(iii)$ Heavy water is more effective solvent than ordinary water.
Which of the above statements are correct?

When chlorine water is exposed to sunlight,$O_2$ is liberated. Hence

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

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