The Chromyl chloride test is performed for the confirmation of the presence of which of the following in a mixture?

$A$ sodium salt gives a white precipitate with $MgCl_2$ only upon heating. What is the anion of the sodium salt?

$A$ salt,which on heating with conc. $H_2SO_4$ gives violet vapours,is

$A$ mixture is heated with dilute $H_2SO_4$ and the lead acetate paper turns black due to the evolved gases. The mixture contains:

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

$A$ white sodium salt dissolves readily in water to give a solution which is neutral to litmus. When silver nitrate solution is added to the aforementioned solution,a white precipitate is obtained which does not dissolve in dilute nitric acid. The anion is: