(a) In the manufacture of benzoic acid from toluene, alcoholic potassium permanganate is used as an oxidant because of the following reasons.

(i) In a neutral medium, ${\mathrm{OH}}^{-}$ ions are produced in the reaction itself. As a result, the cost of adding an acid or a base can be reduced.

(ii) ${\mathrm{KMnO}}_4$ and alcohol are homogeneous to each other since both are polar. Toluene and alcohol are also homogeneous to each other because both are organic compounds. Reactions can proceed at a faster rate in a homogeneous medium than in a heterogeneous medium. Hence, in alcohol, ${\mathrm{KMnO}}_4$ and toluene can react at a faster rate.
The balanced redox equation for the reaction in a neutral medium is give as below:

(b) When conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ is added to an inorganic mixture containing bromide, initially HBr is produced. HBr, being a strong reducing agent reduces ${\mathrm{H}}_2{\mathrm{SO}}_4$to ${\mathrm{SO}}_2$ with the evolution of red vapour of bromine.

$\begin{array}{l}2\mathrm{NaBr}+2{\mathrm{H}}_2{\mathrm{SO}}_4⟶2{\mathrm{NaHSO}}_4+2\mathrm{HBr}\\ 2\mathrm{HBr}+{\mathrm{H}}_2{\mathrm{SO}}_4⟶{\mathrm{Br}}_2+{\mathrm{SO}}_2+2{\mathrm{H}}_2\mathrm{O}\\ \left(\mathrm{red} \mathrm{vapour}\right)\end{array}$

But, when conc. ${\mathrm{H}}_2{\mathrm{SO}}_4$ is added to an inorganic mixture containing chloride, a pungent smelling gas (HCl) is evolved. HCl, being a weak reducing agent, cannot reduce ${\mathrm{H}}_2{\mathrm{SO}}_4$ to ${\mathrm{SO}}_2$.

$2\mathrm{NaCl}+2{\mathrm{H}}_2{\mathrm{SO}}_4\to 2{\mathrm{NaHSO}}_4+2\mathrm{HCl}$