In the brown ring test,the brown color for $NO_2^-$ and $NO_3^-$ is due to the formation of which complex ion?

When a few drops of $KMnO_4$ are added to an acidic solution of an anion,which of the following,if present,will $NOT$ decolorize $KMnO_4$?

$A$ salt is heated first with dil. $H_2SO_4$ and then with conc. $H_2SO_4$. No reaction takes place. It may be

$A$ solution of a salt in dilute $H_2SO_4$ gives a blue color with starch iodide solution. This indicates the presence of which ion?

Molar mass of the salt from $NaBr$,$NaNO_3$,$KI$,and $CaF_2$ which does not evolve coloured vapours on heating with concentrated $H_2SO_4$ is . . . . . . $g \ mol^{-1}$. (Molar mass in $g \ mol^{-1}$: $Na: 23$,$N: 14$,$K: 39$,$O: 16$,$Br: 80$,$I: 127$,$F: 19$,$Ca: 40$)

$A$ salt gives violet vapours when treated with conc. $H_2SO_4$. It contains