Which ion's salt solution produces a violet layer when chlorine water and chloroform are added?

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

In the qualitative analysis of nitrate,a brown ring is formed due to the formation of:

$[X] + H_2SO_4 \to [Y]$ (a colourless gas with irritating smell).
$[Y] + K_2Cr_2O_7 + H_2SO_4 \to$ green solution.
$[X]$ and $[Y]$ are:

How do you account for the following observations?
$(a)$ Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants,yet in the manufacture of benzoic acid from toluene,we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
$(b)$ When concentrated sulphuric acid is added to an inorganic mixture containing chloride,we get a colourless pungent-smelling gas $HCl$,but if the mixture contains bromide,then we get red vapours of bromine. Why?

Which anion of a sodium salt gives a white precipitate upon heating with a magnesium salt?