In thed disproportionation reaction, 3HClO₃$\to$HClO₄ + Cl₂+ 2O₂+H₂O, the equivalent mass of the oxidising agent is (molar mass of HClO₃ = 84.45)

$\stackrel{+5}{2{\mathrm{HClO}}_3}\to \stackrel{+7}{\mathrm{HClO}}+\stackrel{0}{{\mathrm{Cl}}_2}+2{\mathrm{O}}_2+{\mathrm{H}}_2\mathrm{O}$
Since O.N of Cl decreases from +5 in ${\mathrm{HClO}}_3$ to zero in ${\mathrm{Cl}}_2$ therefore, ${\mathrm{HClO}}_3$ acts as the oxidising agent. In other words, O.no decreases by 5 and the equivalent mass of oxidising agent =Mol mass/5 = 84.45/5 = 16.89.