$A$ brown ring appears in the test for

Chromyl chloride vapours are dissolved in $NaOH$ and acetic acid and lead acetate solution is added,then

The brown ring test is used for the detection of which radical?

Given below are two statements:
Statement-$I$: The gas liberated on warming a salt with dil $H_2SO_4$,turns a piece of paper dipped in lead acetate into black,it is a confirmatory test for sulphide ion.
Statement-$II$: In statement-$I$ the colour of paper turns black because of formation of lead sulphite.
In the light of the above statements,choose the most appropriate answer from the options given below:

An anion solution gives a white precipitate with $AgNO_3$ solution. The precipitate dissolves in dilute ammonia due to the formation of:

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