What is Soda ash?

The ionic mobility of alkali metal ions in aqueous solution is maximum for

Which one of the following nitrates will decompose to give $NO_2$ on heating?

Sodium carbonate can be manufactured by Solvay's process,but potassium carbonate cannot be prepared by this method because:

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

When sodium is burnt in moist air,the final product will be: