$P \xrightarrow{\Delta } Q$ (metallic solid) $+ R \uparrow + S \uparrow$
$X \xrightarrow{\Delta } Y$ (amphoteric oxide) $+ R \uparrow + S \uparrow$
$P$ and $X$ are respectively:

When substance $A$ reacts with water,it produces a combustible gas $B$ and a solution of substance $C$ in water. When another substance $D$ reacts with solution $C$,it produces the same gas $B$,even when reacting with dilute sulfuric acid at room temperature. $A$ gives a golden yellow flame in a Bunsen burner flame. What are $A, B, C,$ and $D$ respectively?

$KO_2$ finds use in oxygen cylinders used for space and submarines. The fact$(s)$ related to such use of $KO_2$ is/are:

$Na_2CO_3$ is manufactured by the Solvay process. The products that are recycled are:

$Ca + 2C$ $\rightarrow CaC_2$ $\xrightarrow{N_2, \Delta} A$
Compound $(A)$ is used as a/an:

The correct order of degree of hydration of $M^{+}$ ions of alkali metals is