Which of the following hydrides has the lowest boiling point?

On strong heating,$ZnCl_2 \cdot 2H_2O$ gives .......

Heavy water $(D_2O)$ freezes at $............ \ ^\circ C$.

The products formed when heavy water is reacted with magnesium nitride are:

Statements about heavy water are given below.
$A.$ Heavy water is used in exchange reactions for the study of reaction mechanisms.
$B.$ Heavy water is prepared by exhaustive electrolysis of water.
$C.$ Heavy water has higher boiling point than ordinary water.
$D.$ Viscosity of $H_2O$ is greater than $D_2O$.

Boiling of hard water is helpful in removing the temporary hardness by converting calcium hydrogen carbonate and magnesium hydrogen carbonate to ....