Which of the following does not decolourise iodine?

$A$ solution of $10 \ mL$ of $\frac{M}{10} \ FeSO_4$ was titrated with $KMnO_4$ solution in an acidic medium. The amount of $KMnO_4$ used will be:

Light green crystals of ferrous sulphate lose water molecules and turn brown on exposure to air. This is due to its oxidation to:

$Fe^{3+}$ is reduced to $Fe^{2+}$ by using:
$A$. $H_2O_2$ in presence of $NaOH$
$B$. $Na_2O_2$ in water
$C$. $H_2O_2$ in presence of $H_2SO_4$
$D$. $Na_2O_2$ in presence of $H_2SO_4$

$A$ mixture of potassium chlorate,oxalic acid,and sulphuric acid is heated. During the reaction,which element undergoes the maximum change in its oxidation number?

In order to oxidize a mixture of $1 \text{ mole}$ each of $FeC_2O_4$, $Fe_2(C_2O_4)_3$, $FeSO_4$, and $Fe_2(SO_4)_3$ in an acidic medium, the number of moles of $KMnO_4$ required is: