$p$-Amino- $N, N$-dimethylaniline is added to a strongly acidic solution of ${X}$. The resulting solution is treated with a few drops of aqueous solution of ${Y}$ to yield blue coloration due to the formation of methylene blue. Treatment of the aqueous solution of ${Y}$ with the reagent potassium hexacyanoferrate$(II)$ leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly, treatment of the solution of ${Y}$ with the solution of potassium hexacyanoferrate$(III)$ leads to a brown coloration due to the formation of ${Z}$.
$1.$ The compound ${X}$ is
$(A)$ $\mathrm{NaNO}_3$ $(B)$ $\mathrm{NaCl}$ $(C)$ $\mathrm{Na}_2 \mathrm{SO}_4$ $(D)$ $\mathrm{Na}_2 \mathrm{~S}$
$2.$ The compound ${Y}$ is
$(A)$ $\mathrm{MgCl}_2$ $(B)$ $\mathrm{FeCl}_2$ $(C)$ $\mathrm{FeCl}_3$ $(D)$ $\mathrm{ZnCl}_2$
$3.$ The compound ${Z}$ is
$(A)$ $\left.\mathrm{Mg}_2 \mid \mathrm{Fe}(\mathrm{CN})_6\right]$ $(B)$ $\operatorname{Fe}\left[\mathrm{Fe}(\mathrm{CN})_6\right]$
$(C)$ $\mathrm{Fe}_4\left[\mathrm{Fe}(\mathrm{CN})_6\right]_3$ $(D)$ $\mathrm{K}_2 \mathrm{Zn}_3\left[\mathrm{Fe}(\mathrm{CN})_6\right]_2$
Give the answer question $1,2$ and $3.$
