Which of the following compounds is/are used for oxygenating the submarine or spaceshuttle?

Holme's signals can be obtained by using

Compare the solubility and thermal stability of the following compounds of the alkali metals with those of the alkaline earth metals: $(i)$ Nitrates,$(ii)$ Carbonates,$(iii)$ Sulphates.

Match the average fundamental compounds with their proper percentage present in Portland cement.

Compound	Percentage proportion
$1. CaO$	$d. 50-60\%$
$2. Al_2O_3$	$a. 5-10\%$
$3. SO_3$	$b. 1-3\%$

The correct statements among the following are:
$(A)$ $BeH_2$ and $MgH_2$ are polymeric in nature.
$(B)$ $LiH$ is unreactive to oxygen at moderate temperatures.
$(C)$ $BeH_2$ and $MgH_2$ possess significant covalent character.
$(D)$ The stability of alkali metal hydrides follows the order $LiH < NaH < KH < RbH < CsH$.

$\underbrace{HgI_2}_{X}$ $\xrightarrow[\text{Sublimation}]{\Delta} \underbrace{HgI_2}_{Y}$ $\xrightarrow[\text{On rubbing}]{\text{Cooling}} \underbrace{HgI_2}_{Z}$