Find the compound $A$ from the following reaction sequences:
$A$ $\xrightarrow{\text{aqua-regia}} B$ $\xrightarrow[(2) CH_3COOH]{(1) KNO_2 \mid NH_4OH} \text{yellow ppt}$

Identify the inorganic sulphides that are yellow in colour $ : $
$(A)$ $(NH_4)_2S$
$(B)$ $PbS$
$(C)$ $CuS$
$(D)$ $As_2S_3$
$(E)$ $As_2S_5$
Choose the correct answer from the options given below $ : $

$p$-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
$(A)$ $NaNO_3$ $(B)$ $NaCl$ $(C)$ $Na_2SO_4$ $(D)$ $Na_2S$
$2.$ The compound $Y$ is
$(A)$ $MgCl_2$ $(B)$ $FeCl_2$ $(C)$ $FeCl_3$ $(D)$ $ZnCl_2$
$3.$ The compound $Z$ is
$(A)$ $Mg_2[Fe(CN)_6]$ $(B)$ $Fe[Fe(CN)_6]$
$(C)$ $Fe_4[Fe(CN)_6]_3$ $(D)$ $K_2Zn_3[Fe(CN)_6]_2$
Give the answer for questions $1, 2$ and $3$.

Which reagent is used to distinguish between silver and lead salts?

In the analysis of Group-$II$ basic radicals,$H_2S$ gas is passed in the presence of dilute $HCl$ because...

Which of the following options is incorrect?