An element $A$ of group $1$ shows similarity to an element $B$ belonging to group $2$. If $A$ has maximum hydration enthalpy in group $1$,then $B$ is:

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?

One of the by-products formed during the recovery of $NH_{3}$ from the Solvay process is ..... .

Comment on each of the following observations:
$(a)$ The mobilities of the alkali metal ions in aqueous solution are $Li^{+} < Na^{+} < K^{+} < Rb^{+} < Cs^{+}$
$(b)$ Lithium is the only alkali metal to form a nitride directly.
$(c)$ The standard electrode potential $E^{\circ}$ for the reaction $M^{2+}_{(aq)} + 2e^{-} \to M_{(s)}$ (where $M = Ca, Sr$ or $Ba$) is nearly constant.

$NH_3 + CO_2 + H_2O \to A$
$A + H_2O + CO_2 \to B$
$B + NaCl \to C + NH_4Cl$
$C \xrightarrow{\Delta} D + H_2O + CO_2$
Identify the incorrect statement.

Sodium chloride gives a golden yellow flame in a Bunsen burner. What can be inferred from this?