Acidified $KMnO_4$ can be decolourised by

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_2S_2O_3 + BaCl_2 \longrightarrow BaS_2O_3 \downarrow + 2NaCl$

$KMnO_4$ oxidises $S_2O_3^{2-}$ to $SO_4^{2-}$ in medium $x$ and $NO_2^-$ to $NO_3^-$ in medium $y$. $x$ and $y$ are respectively:

Equivalent weights of $KMnO_4$ and $K_2Cr_2O_7$ in acidic medium are respectively. (Molecular weight of $KMnO_4 = M_A$ and Molecular weight of $K_2Cr_2O_7 = M_B$).

Which one of the following conversions does not involve either oxidation or reduction?

Which of the following reactions are redox reactions?
$I. \, Cr_2O_7^{2-} + 2OH^- \to 2CrO_4^{2-} + H_2O$
$II. \, Zn + CuSO_4 \to ZnSO_4 + Cu$
$III. \, 2MnO_4^- + 3Mn^{2+} + 4OH^- \to 5MnO_2 + 2H_2O$
$IV. \, 2Cu^+ \to Cu + Cu^{2+}$