Which of the following reactions is $NOT$ an example of a redox reaction?

Which of the following combinations of reagents does not undergo a redox reaction in an aqueous medium?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_2CrO_4 + AgF \longrightarrow Ag_2CrO_4 \downarrow + NaF$

$A$ white crystalline salt $[A]$ reacts with dilute $HCl$ to produce a suffocating gas $[B]$ and also forms a yellow precipitate. When gas $[B]$ is passed through acidified potassium dichromate,it turns the solution green,forming $[C]$. Identify $A, B$,and $C$ respectively.

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$MnS(s) + 2HCl(aq) \longrightarrow MnCl_2(aq) + H_2S(g)$

$H_2S$ ($5$ moles) reacts completely with acidified aqueous potassium permanganate solution. In this reaction,the number of moles of water produced is $x$,and the number of moles of electrons involved is $y$. The value of $(x+y)$ is. . . . . .