Which of the following ions produces violet vapors upon reaction with concentrated $H_2SO_4$?

Assign $A, B, C, D$ from the given type of reaction.
$BaSO_4 \downarrow + dil. HCl$ $(Excess)$ $\longrightarrow$ No reaction

In the chromyl chloride test,the reagent used is

$A$ sodium salt on treatment with $MgCl_2$ gives white precipitate only on heating. The anion of the sodium salt is

The brown ring test is used to detect the presence of which of the following ions?

When $BaCl_{2}$ is added to an aqueous salt solution, a white precipitate is obtained. The anion among $CO_{3}^{2-}$, $SO_{3}^{2-}$, and $SO_{4}^{2-}$ that was present in the solution can be