Which of the following methods is used for the removal of temporary hardness of water?

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:

Which of the following pairs of ions causes hardness in water?

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

Which of the following is not true about the $H_2O$ molecule?

Exhausted permutit is