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

Which pairs of ions are responsible for hardness of water?

$A$ sample of water contains $Mg(HCO_3)_2$ and $Ca(HCO_3)_2$. On boiling this water, these hydrogen carbonates are removed as precipitates. The precipitates are

The solubility of an ionic compound is compared in heavy water $(D_2O)$ and simple water $(H_2O)$. It is:

Observe the following statements:
$1.$ Heavy water is harmful for the growth of animals.
$2.$ Heavy water reacts with $Al_4C_3$ and forms $\text{deuterated acetylene}$.
$3.$ $BaCl_2 \cdot 2D_2O$ is an example of $\text{interstitial deuterate}$.
The correct statements are:

Amongst the following,the form of water with the lowest ionic conductance at $298 \ K$ is