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

Which ion produces a brown gas when the mixture is heated with $MnO_2$ and concentrated $H_2SO_4$?

Which anion's aqueous solution gives a white precipitate with $AgNO_3$,which is soluble in excess $NH_4OH$?

Given below are two statements:
Statement $I$: Griess-Ilosvay test is used for the detection of nitrite ion,which involves the use of sulphanilic acid and $\alpha$-naphthylamine reagent.
Statement $II$: In the above test,sulphanilic acid is diazotized by the acidified nitrite ion,which on further coupling with $\alpha$-naphthylamine forms an azo-dye.
In the light of the above statements,choose the correct answer from the options given below.

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

$A$ 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