Acidified potassium permanganate solution is decolourised  by

$\begin{array}{l}2{\mathrm{KMnO}}_4+3{\mathrm{H}}_2{\mathrm{SO}}_4\to \\ {\mathrm{K}}_2{\mathrm{SO}}_4+2{\mathrm{MnSO}}_4+3{\mathrm{H}}_2\mathrm{O}+\left[\mathrm{O}\right]\\ \left.2{\mathrm{FeSO}}_4+{\mathrm{H}}_2{\mathrm{SO}}_4+\left[\mathrm{O}\right]\to {\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3+{\mathrm{H}}_2\mathrm{O}\right]\times 5\\ [\mathrm{Mohr}-\text{ salt }]\\ 2{\mathrm{KMnO}}_4+10{\mathrm{FeSO}}_4+8{\mathrm{H}}_2{\mathrm{SO}}_4\to \\ {\mathrm{K}}_2{\mathrm{SO}}_4+2{\mathrm{MnSO}}_4+5{\mathrm{Fe}}_2{\left({\mathrm{SO}}_4\right)}_3+8{\mathrm{H}}_2\mathrm{O}\end{array}$

Mohr-salt reducing agent  ${\mathrm{KMnO}}_4/{\mathrm{H}}^{+}\to$ oxidising agent.