Which of the following decolourises the colour of acidic $KMnO_4$?

Assign $A, B, C, D$ from the given type of reaction.
$Ba(NO_3)_2 + Na_2SO_4 \longrightarrow BaSO_4 \downarrow + 2NaNO_3$

When a manganous salt is fused with a mixture of $KNO_3$ and solid $NaOH$, the oxidation number of $Mn$ changes from $+2$ to:

$A$ few drops of $KMnO_4$ solution are added to an acidic solution containing an anion. Which of the following,if present,will $NOT$ cause a change in the color of the $KMnO_4$ solution?

Assign $A, B, C, D$ from the given type of reaction.
$2KI + HgI_2 \downarrow \longrightarrow K_2[HgI_4]$

Which of the following reactions will lead to a redox reaction?