$[X] +$ dil. $H_{2}SO_{4} \longrightarrow [Y]:$
Colourless,suffocating gas
$[Y] + K_{2}Cr_{2}O_{7} + H_{2}SO_{4} \longrightarrow$
Green colouration of solution
Then,$[X]$ and $[Y]$ are

Select the $CORRECT$ statement based on the following reactions:
$\text{Salt } 'X' (\text{soluble}) + \text{dil. } H_2SO_4 \to \text{gas } (B) + \text{neutral oxide } (C) + 'Y'$
$\text{Salt } 'X' (\text{soluble}) \xrightarrow{BaCl_2 \text{ solution}} \text{White ppt. } 'Z'$
$\text{aq. sol. of gas } (B) \xrightarrow{H_2S(g)} 'Y' + \text{neutral oxide } (C)$
Given these reactions,identify the correct statement regarding salt $'X'$.

$A$ 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?

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:

Which one of the following anions is not easily removed from aqueous solutions by precipitation?

$A$ salt gives violet vapours when treated with conc. $H_2SO_4$. It contains