Manganese ions (Mn²⁺ ) can be oxidised by Persulphate ions ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ according to the following half-equations,
$\begin{array}{l}{\mathrm{S}}_2{\mathrm{O}}_8^{2-}+2{\mathrm{e}}^{-}⟶2{\mathrm{SO}}_4^{2-}\\ {\mathrm{Mn}}^{2+}+4{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{MnO}}_4^{-}+8{\mathrm{H}}^{+}+5{\mathrm{e}}^{-}\end{array}$
How many moles of ${\mathrm{S}}_2{\mathrm{O}}_8^{2-}$ are required to oxidise 1 mole of Mn²⁺?