Which of the following will not produce a precipitate with $AgNO_3$ solution?

Among the following observations, the correct one that differentiates between $SO_{3}^{2-}$ and $SO_{4}^{2-}$ is:

$A$ sodium salt gives a white precipitate with $MgCl_2$ only upon heating. What is the anion of the sodium salt?

Choose the correct matching $:-$

Column-$I$	Column-$II$
$P$. $NaBr + \text{Conc. } H_2SO_4 \rightarrow$	$A$. Colourless gas
$Q$. $Na_2S + \text{dil. } HCl \rightarrow$	$B$. Brown colour
$R$. $NaNO_2 + \text{dil. } HCl \rightarrow$	$C$. Rotten egg smell
$S$. $NaNO_3 + \text{Conc. } H_2SO_4 \rightarrow$	$D$. Paramagnetic

$A$ salt,which on heating with conc. $H_2SO_4$ gives violet vapours,is

$[X] +$ 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