A mixture of chlorides of copper, cadmium, chromium, iron and aluminium was dissolved in water.

It was acidified with dilute $\mathrm{HCl}$ and then hydrogen sulphide gas was passed for a sufficient time.

It was filtered, boiled and a few drops of nitric acid were added, while boiling. To this solution, ammonium chloride and ammonium hydroxide were added. To this, an excess of sodium hydroxide was added and then filtered. The filtrate shall give the test for:

${\mathrm{CrO}}_4^{2-}+{\mathrm{H}}^{+}+{\mathrm{H}}_2{\mathrm{O}}_2\stackrel{ \mathrm{ether}}{⟶}\mathrm{X}+{\mathrm{H}}_2\mathrm{O}$

Identify the correct statement with respect to $\mathrm{X}$.

A coloured solution of a salt gives the following reactions:

(i) It gives a white precipitate with sodium hydroxide, which becomes brown on exposure to air.

(ii) It gives a white precipitate with ammonia solution, which is soluble in ammonium salts.

(iii) Its acidified solution containing a few drops of dilute ${\mathrm{AgNO}}_3$ on boiling with ammonium peroxodisulphate gives a reddish-violet solution. The cation of the salt is: