$A$ substance reacts with dilute $H_2SO_4$ to release a colorless gas,which turns baryta water $[Ba(OH)_2]$ turbid and decolorizes an acidic solution of dichromate. The presence of which of the following is indicated by this reaction?

$S^{2-}$ and $SO_3^{2-}$ can be distinguished by using

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:

$Na_2CO_3$ cannot be used to identify which of the following ions?

Aqueous solution of a salt $(A)$ forms a dense white precipitate with $BaCl_{2}$ solution. The precipitate dissolves in dilute $HCl$ to produce a gas $(B)$ which decolourises acidified $KMnO_{4}$ solution. $A$ and $B$ respectively are

Assertion $(A) :- Fe^{+3}$ is not used in the brown ring test for $NO_3^{-}$.
Reason $(R) :-$ Reduction of $NO_3^{-}$ takes place during the test.