$M \text{ (Salt)} + \text{Dil. } HCl \xrightarrow{\text{Warm}} N \uparrow + P \downarrow$. Gas $N$ changes the colour of $FeSO_4$ solution into a yellow solution. Then,salt $M$ in the above reaction is:

The reagent$(s)$ that can selectively precipitate $S^{2-}$ from a mixture of $S^{2-}$ and $SO_4^{2-}$ in aqueous solution is(are):
$(A)$ $CuCl_2$
$(B)$ $BaCl_2$
$(C)$ $Pb(CH_3COO)_2$
$(D)$ $Na_2[Fe(CN)_5NO]$

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

The brown ring test is used for the detection of which of the following?

The Chromyl chloride test is performed for the confirmation of the presence of which of the following in a mixture?

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: