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

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 $K_2Cr_2O_7 = M_B$).

$40 \text{ mL}$ of $x \text{ M } KMnO_4$ solution is required to react completely with $200 \text{ mL}$ of $0.02 \text{ M}$ oxalic acid solution in acidic medium. The value of $x$ is:

$H_2S$ acts only as a reducing agent while $SO_2$ can act both as a reducing and oxidizing agent because

Ferrous sulphate on strong heating gives:

Assign $A, B, C, D$ from the given type of reaction.
$ZnSO_4 \, (aq) + MgCl_2 \, (aq) \longrightarrow$ No reaction