Heavy water is used in an atomic reactor as:

Select the correct statement about water.
$(i)$ Critical temperature of $H_2O$ is less than $NH_3$.
$(ii)$ Standard boiling point of water is $100 \ ^oC$.
$(iii)$ Critical volume of $H_2O$ is less than $NH_3$.

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

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

The temporary hardness of a water sample is due to compound $X$. Boiling this sample converts $X$ to compound $Y$. $X$ and $Y$,respectively,are

Water is oxidised to oxygen by

$D_2O$ is preferred to $H_2O$ as a moderator in nuclear reactors because: