The redox reaction among the following is

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Cu^{2+} (aq.) + 2I^{-} \longrightarrow CuI \downarrow + \frac{1}{2}I_2$

$A$ 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.

What is the equivalent weight of the reductant in the reaction $2[Fe(CN)_6]^{3-} + H_2O_2 + 2OH^{-} \rightarrow 2[Fe(CN)_6]^{4-} + 2H_2O + O_2$? (Given: $Fe = 56, C = 12, N = 14, O = 16, H = 1$)

Among $C$,$S$,and $P$,the element$(s)$ that produce$(s)$ $SO_{2}$ on reaction with hot conc. $H_{2}SO_{4}$ is / are

Consider the following redox reaction in basic medium.
$x \ Cr(OH)_3 + y(IO_3)^{-} + z(OH)^{-} \rightarrow a(CrO_4)^{2-} + b(I)^{-} + c(H_2O)$
The incorrect option about it is