Calcium hydride on hydrolysis forms?

What causes the temporary and permanent hardness of water?

The $O-H$ bond length in $H_2O$ in the gas phase is: (in $pm$)

Explain: Proton $(H^{+})$ does not exist in aqueous solution.

Find the number of $CORRECT$ order against mentioned property :-
$(i)$ $D_2O = H_2O$ (number of electrons)
$(ii)$ $D_2O > H_2O$ $(|\Delta H_f|)$
$(iii)$ $D_2O > H_2O$ $(|\Delta H_{vaporization}|)$
$(iv)$ $D_2O > H_2O$ (density)
$(v)$ $D_2O > H_2O$ (Molecular mass)

The products obtained during the treatment of hard water using Clark's method are: