If zinc pieces are added to yellow $FeCl_3$ solution,it turns to very light green. It is because

If stoichiometric quantities of a $KMnO_4$ and $K_2Cr_2O_7$ mixture are added for the oxidation of $Fe^{2+}$ to $Fe^{3+}$ in an acidic medium,then $Fe^{2+}$ will be oxidized:

In the reaction,$4Fe + 3O_2 \to 4Fe^{3+} + 6O^{2-}$,which of the following statements is incorrect?

How do you account for the following observations?
$(a)$ Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants,yet in the manufacture of benzoic acid from toluene,we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
$(b)$ When concentrated sulphuric acid is added to an inorganic mixture containing chloride,we get a colourless pungent-smelling gas $HCl$,but if the mixture contains bromide,then we get red vapour of bromine. Why?

Ferrous sulphate on strong heating gives:

$PbO$ and $PbO_2$ react with $HCl$ according to the following chemical equations:
$(i)$ $2PbO + 4HCl \to 2PbCl_2 + 2H_2O$
$(ii)$ $PbO_2 + 4HCl \to PbCl_2 + Cl_2 + 2H_2O$
Why do these compounds differ in their reactivity?