$$ \mathrm{CaC}_2+2 \mathrm{D}_2 \mathrm{O} \longrightarrow " P^{\prime \prime}+\mathrm{Ca}(\mathrm{OD})_2 $$

In the above reaction, product " $P$ " is

Deionised water is obtained by passing hard water through

The correct statements among the following are

(A) $\mathrm{BeH}_2$ and $\mathrm{MgH}_2$ are polymeric in nature.

(B) LiH is unreactive to oxygen, at moderate temperatures.

(C) $\mathrm{BeH}_2$ and $\mathrm{MgH}_2$ possesses significant covalent character.

(D) The stability of alkali hydrides follows the order $\mathrm{LiH}<\mathrm{NaH}< \mathrm{KH}<\mathrm{RbH}<\mathrm{CsH}$.