To a solution of a colourless sodium salt,a solution of lead nitrate was added to form a white precipitate which dissolves in warm water and reprecipitates on cooling. Which of the following acid radicals is present in the salt?

When a solution of a mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in an acidic medium,a dark brown ring was formed,whereas on treatment with neutral $FeCl_3$,it gave a deep red colour which disappeared on boiling and a brown-red precipitate was formed. The mixture contains:

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

$A$ 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:

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

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