Write the redox reaction that occurs when a zinc rod is placed in a $H_2SO_4$ solution.

Balance the following redox reactions by the ion-electron method:
$(a)$ $MnO_4^-(aq) + I^{-}(aq) \rightarrow MnO_2(s) + I_2(s)$ (in basic medium)
$(b)$ $MnO_4^-(aq) + SO_2(g) \rightarrow Mn^{2+}(aq) + HSO_4^-(aq)$ (in acidic solution)
$(c)$ $H_2O_2(aq) + Fe^{2+}(aq) \rightarrow Fe^{3+}(aq) + H_2O(l)$ (in acidic solution)
$(d)$ $Cr_2O_7^{2-} + SO_2(g) \rightarrow Cr^{3+}(aq) + SO_4^{2-}(aq)$ (in acidic solution)

$6 \times 10^{-3}$ mole $K_2Cr_2O_7$ reacts completely with $9 \times 10^{-3}$ mole $X^{n+}$ to give $XO_3^-$ and $Cr^{3+}$. The value of $n$ is

$ClO_2$ oxidizes $H_2O_2$ to $O_2$ in basic medium and is itself reduced to $Cl^-$. How many moles of $H_2O_2$ will be oxidized by one mole of $ClO_2$ (in $.5$)?

In the neutral or faintly alkaline medium,$KMnO_4$ oxidises iodide into iodate. The change in oxidation state of manganese in this reaction is from?

What is formed when Iodine is absorbed by hypo solution?