Sodium sulphite on heating with dilute $HCl$ liberates a gas which

Explain the brown ring test for nitrate ions.

$A$ salt solution is treated with chloroform drops. Then it is shaken with chlorine water. The chloroform layer becomes violet. The solution contains:

$A$ white crystalline salt $A$ reacts with dilute $HCl$ to liberate a suffocating gas $B$ and also forms a yellow precipitate. The gas $B$ turns potassium dichromate acidified with dilute $H_{2}SO_{4}$ to a green coloured solution $C$. $A$,$B$ and $C$ are respectively

Which of the following ions will not give a precipitate with $AgNO_3$?

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