Which of the following substances releases $SO_2$ gas upon reaction with dilute $H_2SO_4$?

$[X] + H_2SO_4 \rightarrow [Y]$ (a colorless gas with a pungent smell). $[Y] + K_2Cr_2O_7 + H_2SO_4 \rightarrow$ green solution. What are $[X]$ and $[Y]$?

An aqueous solution of a salt,when treated with $AgNO_3$ solution,gives a white precipitate which dissolves in $NH_4OH$. The radical present in the salt is:

$X + H_2SO_4 \to Y$ (a colorless gas with a pungent smell).
$Y + K_2Cr_2O_7 + H_2SO_4 \to$ green colored solution.
What are $X$ and $Y$?

$A$ white sodium salt dissolves readily in water to give a solution which is neutral to litmus. When silver nitrate solution is added to the aforementioned solution,a white precipitate is obtained which does not dissolve in dilute nitric acid. The anion is:

When $BaCl_2$ is added to a clear solution of a compound $(X)$,a heavy white precipitate is formed which does not dissolve in $dil. HCl$. What is the compound $(X)$?