$A$ mixture is heated with dilute $H_2SO_4$ and the lead acetate paper turns black due to the evolved gases. The mixture contains:

Sodium nitroprusside,when added to an alkaline solution of sulphide ions,produces a purple colour due to the formation of:

In the chromyl chloride test,the reagent used is

$A$ salt gives violet vapours when treated with concentrated $H_2SO_4$,it contains

When $Y$ is treated with $KMnO_4$,then the final precipitate is of:
$'X' \xrightarrow[BaCl_{2} \text{ solution}]{} 'Y' \quad (\text{White ppt., insoluble in dil. } HCl)$
$'X' \xrightarrow[\text{Flame test}]{} \text{Golden yellow flame}$

During the detection of an acidic radical present in a salt,a student obtains a pale yellow precipitate that is soluble with difficulty in $NH_4OH$ solution when the sodium carbonate extract is first acidified with dil. $HNO_3$ and then $AgNO_3$ solution is added. This indicates the presence of: