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

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

$A$ substance on treatment with dilute $H_2SO_4$ liberates a colourless gas which produces:
$(i)$ turbidity with baryta water and
$(ii)$ turns acidified dichromate solution green.
The reaction indicates the presence of:

When chlorine water is added to an aqueous solution of potassium halide in the presence of chloroform,a violet colour is obtained. On adding more chlorine water,the violet colour disappears,and a colourless solution is obtained. This test confirms the presence of which of the following in the aqueous solution?

$Na_2CO_3$ cannot be used to identify which of the following ions?

$A$ mixture when heated with conc. $H_2SO_4$ and $MnO_2$ produces brown fumes due to the presence of: